Дисертації: "Terahertz gas phase spectroscopy"

1

Zhang, Yaqing Ph D. Massachusetts Institute of Technology. "Two-dimensional terahertz rotational spectroscopy in the gas phase." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122715.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references.
Two-dimensional (2D) coherent spectroscopy has been developed to study molecular dynamics and structures for decades, but its extension into the terahertz (THz) regime remains rare. In this thesis, I describe several experiments using two-dimensional terahertz rotational spectroscopy. Employing intense THz electromagnetic fields and the differential chopping technique, we have extended multi-dimensional coherent spectroscopy into the THz regime. We have observed rotational dynamics of linear, symmetric-top, and asymmetric-top molecular species, indicating that 2D THz spectroscopy is an incisive tool for investigating collective quantum effects of the rotational degree of freedom. Based on the quantum mechanical rigid rotor model, we have developed simulation and calculation approaches to disentangling spectroscopic signals from molecular rotations.
We have shown ultrafast 2D THz photon echo spectroscopy of gaseous acetonitrile samples, revealing J-state-resolved rotational dynamics in symmetric-top molecular rotors. We have revealed nonlinear rotational couplings and many-body interactions in water vapor, uncovering the strongly correlated nature of rotational quantum states in water molecules. Additionally, experimental evidence of linear and nonlinear THz spectroscopy of stable water dimers in the vicinity of atmospheric conditions has been observed. We have reported dual-type rotational couplings and a propensity for the K-state-dependent cross-peaks in sulfur dioxide, highlighting distinct rotational properties in slightly asymmetric-top molecules. We have measured the quartic THz effect using two-dimensional THz-Raman hybrid spectroscopy, opening the way for understanding and applications of higher-even-order THz-matter coherences beyond the linear and quadratic THz field effects.
Utilizing the density matrix and time propagation approaches, we have developed a set of simulation and calculation methodologies to characterize rotational dynamics in the gas phase based on the quantum mechanical rigid-rotor model. Our work shows the remarkable capability of 2D THz spectroscopy to interrogate rotational dynamics in the gas phase, laying a foundation for understanding and manipulation of nonlinear light-molecule interactions via multi-dimensional coherent THz spectroscopy.
by Yaqing Zhang.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry

2

Mahé, Jérôme. "Far infrared/Tera-Hertz spectroscopy in the gas phase : experiments and theory." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLE043/document.

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La spectroscopie infrarouge permet d’identifier la structure 3D de systèmes moléculaires, par comparaison des spectres mesurés et simulés. Nous travaillons en phase gazeuse, où les molécules et clusters sont libres d’interactions intermoléculaires. Notre travail combine les expériences IR-UV ion-dip et le calcul de spectres IR anharmoniques par la méthode DFT-MD. Le spectre IR est calculé pour les structures 3D de plus basses énergies,le meilleur accord donnant la connaissance de la structure présente dans les conditions expérimentales.Nous démontrons que le domaine de l’IR lointain/THz (<800 cm-1, <24 THz) permet d’identifier sans ambiguïté la structure 3D de molécules et clusters en phase gazeuse, là ou les signatures du domaine 1000-4000 cm-1 peuvent être limitées. Les systèmes considérés sont des dipeptides, un modèle de feuillet β, dérivés du phénol (et complexés à l’eau) des paires de bases de l’ADN, dont les structures sont bâties sur des liaisons hydrogène intra/intermoléculaires
Infrared spectroscopy allows the assignment of three dimensional structures of molecular systems, by comparing experimental and theoretical spectra. Our investigations take place in the gas phase, where molecules and clusters are free of intermolecular interactions.Our work combines experimental IR-UV ion dip spectroscopy and theoretical DFT-MD anharmonic spectroscopy. The infrared spectrum is calculated for low energy 3Dstructures and the best match between theory and experiment provides the information about the structure present in the experimental conditions.We demonstrate for several systems that far infrared/THz spectroscopy (<800 cm-1, <24THz) allows conformational assignment without ambiguities, contrary to the more traditional 1000-4000 cm-1 range. Systems investigated here are dipeptides, a β-sheet model, phenol derivatives (also complexe dwith water molecules), DNA base pairs, all these structures being built on intra-/intermolecular hydrogen bonds

3

Elmaleh, Coralie. "Développement d’un prototype ultrasensible d’analyse de gaz dans le domaine submillimétrique." Electronic Thesis or Diss., Littoral, 2024. http://www.theses.fr/2024DUNK0698.

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Cette thèse explore le développement technologique d'une expérience spectroscopique dans le domaine submillimétrique, aussi connu sous le nom de Terahertz (THz). Cette bande spectrale se distingue par sa capacité à résoudre finement des doublets moléculaires, permettant une identification précise et claire de mélanges gazeux complexes, même lorsque d'autres longueurs d'onde pourraient échouer.Bien que la région THz offre un pouvoir de résolution exceptionnel, les spectromètres qui y opèrent sont souvent confrontés à des défis de sensibilité en raison du développement de la technologie dans cette bande. Grâce à une approche innovante, nous avons mis en œuvre la première expérience de Cavity ring-down Spectroscopy (CRDS) capable de quantifier des composés avec une précision allant jusqu’au ppb. L'étude est concentrée entre 550 GHz et 650 GHz, une fenêtre du spectre THz qui non seulement offre une résolution et une sensibilité moléculaire inégalées, mais possède aussi la capacité de pénétrer des matériaux non conducteurs tout en étant non ionisante. Ces propriétés positionnent cette technologie à la pointe des outils d'analyse, promettant une pléthore d'applications, allant de la recherche fondamentale à des applications industrielles
This thesis explores the technological development of a spectroscopic experiment in the submillimeter range, also known as Terahertz (THz). This spectral band stands out for its ability to precisely resolve molecular doublets, enabling clear and precise identification of complex gas mixtures, even when other wavelengths might fail.Although the THz region offers exceptional resolving power, spectrometers operating in this region often face sensitivity challenges due to the development of technology in this band. Thanks to an innovative approach, we have implemented the first Cavity Ring-Down Spectroscopy (CRDS) experiment capable of quantifying compounds to ppb precision. The study is concentrated between 550 GHz and 650 GHz, a window of the THz spectrum that not only offers unrivalled resolution and molecular sensitivity, but also possesses the ability to penetrate non-conducting materials while being non-ionizing. These properties position this technology at the cutting edge of analysis tools, promising a plethora of applications, from fundamental research to industrial applications

4

Marcinkiewicz, Michal. "Terahertz Spectroscopy of Topological Phase Transitions in HgCdTe-based systems." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS068/document.

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Cette thèse porte sur l'exploration de différentes phases topologiques présentes dans des hétérostructures à base de mercure, cadmium et tellure (HgCdTe). Ces systèmes sont de parfaits cas d'études des états topologiques dans la matière condensée. En effet, leur structure de bande peut aisément être modifiée d'inversée à non-inversée par le biais de paramètres internes ou externes.Lorsqu'un système présente une structure de bande inversée, il a une topologie non triviale. Il est impossible de modifier cet ordre topologique sans fermer son gap, ce qui inévitablement entraîne l'apparition de particules sans masse dans son volume. Un système présentant une structure de bande inversée et un gap d'énergie finie dans lequel se trouve le niveau de Fermi, est appelé isolant topologique. Ce nouveau type de matériau est isolant dans son volume, mais abrite des états métalliques sans gap sur ses bords. Ces derniers ont une relation de dispersion linéaire et sont protégés des effets liés au désordre et de la rétrodiffusion par des impuretés non magnétiques. Ces états particuliers apparaissent à l'interface de matériaux présentant des ordres topologiques différents. Ainsi, un isolant topologique 2D se caractérise par des canaux 1D de conductance polarisés en spin à ses bords, alors qu'un isolant topologique 3D accueille des fermions de Dirac 2D, polarisés en spin, aux surfaces.L'existence de fermions sans masse 2D et 3D a déjà été démontrée expérimentalement. Cependant, la transition de phase topologique durant laquelle apparaissent les particules sans masse n'a que très peu été explorée. Il est possible de modifier la structure de bande de HgCdTe d'inversée à non inversée par le biais de la composition chimique, la pression, la température ou le confinement quantique. Ces paramètres permettent ainsi de sonder le système au voisinage de différentes transitions de phase topologiques. Dans ce travail, l'utilisation de la température comme paramètre d'ajustement continu du gap permet d'étudier au point de transition de phase l'apparition de fermions semi-relativistes de Dirac (2D) et de Kane (3D) ainsi que leurs propriétés.Les systèmes étudiés au cours de ces travaux de recherche sont des cristaux massifs de Hg1-xCdxTe et des puits quantiques HgTe/CdTe présentant des structures de bandes inversées et non inversées, ainsi que des couches minces de HgTe contraintes pouvant être considérées comme des isolants topologiques 3D ayant un confinement quantique résiduel. Tous ces systèmes possèdent des propriétés topologiques. L'interprétation des résultats s'appuie sur les prédictions théoriques basées sur le modèle de Kane. En annexe, une vue d'ensemble des puits quantiques composites InAs/GaSb, structures également identifiées comme isolants topologiques, est présentée, comportant les résultats préliminaires obtenus sur ces dernières.Toutes les structures ont été étudiées par magnétospectroscopie en transmission dans les domaines de fréquence terahertz et infra-rouge moyen à l'aide d'un dispositif expérimental spécifiquement conçu pour permettre des mesures sur une large plage de températures
This thesis presents an investigation of different topological phases in mercury-cadmium-telluride (HgCdTe or MCT) based heterostructures. These solid state systems are indeed a perfect playground to study topological states, as their band structure can be easily varied from inverted to non-inverted, by changing internal or external parameters.If a system has an inverted band ordering, its electronic structure has a non-trivial topology. One cannot change its topological order without closing the band gap, which is inevitably accompanied with the appearance of massless particles in the bulk. A system, that has an inverted band structure and a finite gap in which the Fermi level is positioned, is called a topological insulator. These novel materials are insulators in the bulk, but host gapless metallic states with linear dispersion relation at boundaries, protected against disorder and backscattering on non-magnetic impurities. These states arise at the interfaces between materials characterized by a different topological order. A 2D topological insulator is thus characterized by a set of 1D spin-polarized channels of conductance at the edges, while a 3D topological insulator supports spin-polarized 2D Dirac fermions on its surfaces.The 2D and 3D massless fermions have already been demonstrated experimentally in HgCdTe-based heterostructures. However, the topological phase transitions during which the massless particles appear remain barely explored. The HgCdTe band structure can be tuned from inverted to non-inverted using chemical composition, pressure, temperature, or quantum confinement. These parameters therefore allow to probe the system in the vicinity of different topological phase transitions. In this thesis, the use of temperature as continuous band gap tuning parameter allows to study the appearance and the parameters of semi-relativistic 2D Dirac and 3D Kane fermions emerging at the points of phase transitions.The systems investigated were Hg$_{1-x}$Cd$_x$Te bulk systems and HgTe/CdTe quantum wells characterized by an inverted and regular band order, and strained HgTe films which can be considered as 3D topological insulators with a residual quantum confinement. All these systems exhibit topological properties, and the experimental results are interpreted according to theoretical predictions based on the Kane model. This thesis is complemented by an overview and the preliminary results obtained on a different compound -- a InAs/GaSb broken-gap quantum well, which was also identified as a topological insulator. The structures were studied by means of terahertz and mid-infrared magneto-transmission spectroscopy in a specifically designed experimental system, in which temperature could be tuned in a broad range

5

Colarusso, Pina. "Selected projects in gas-phase spectroscopy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22196.pdf.

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6

Puskar, Ljiljana. "Gas phase ligand field photofragmentation spectroscopy." Thesis, University of Sussex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394258.

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7

Phillips, Alexander John. "High resolution and sensitivity gas phase spectroscopy." Thesis, Queen Mary, University of London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267656.

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8

Faulk, James Donald. "Spectroscopy and photodynamics of gas phase ions." Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1055789262.

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9

Zhang, Keqing. "Infrared spectroscopy of molecules in the gas phase." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21402.pdf.

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10

Schubert, J. E. "High-resolution spectroscopy of small gas-phase radicals." Thesis, University of Southampton, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354301.

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11

O'Brien, Leah Christine. "Laser and Fourier transform spectroscopy of gas phase molecules." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184305.

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Laser and Fourier transform spectroscopy were used to study a variety of gas phase molecules. A series of calcium and strontium monoalkoxides, CaOR and SrOR [R=H, CH₃, CH₂CH₃, CH(CH₃)₂, CH₂CH₂CH₃, CH₂(CH₂)₂CH₃, CH₂(CH₃)CH₂CH₃ and C(CH₃)₃] was studied by laser induced fluorescence and laser excitation techniques. The A - X and B - X electronic transitions were recorded. Calcium and strontium monocyclopentadienide, CaCp and SrCp, were produced in a Broida oven and the spectra were recorded at low resolution by laser techniques. The geometry of these molecules is like an "open-faced sandwich", with C₅ᵥ symmetry. The A²Π - X²Σ⁺ and B²Σ⁺ - X²Σ⁺ transitions of calcium and strontium monoisocyanate, CaNCO and SrNCO, were recorded for the first time. The spectra are interpreted as arising from a molecule with linear, ionic Sr⁺ - ⁻NCO structure. The 0-0 band of the A - X transition of SrNCO was recorded at high resolution and rotationally analyzed. The use of a 0.64 m monochromator, acting as a narrow bandpass filter, was necessary for recording the spectra and enabled the correct assignment of the rotational lines. By comparing the molecular constants of SrNCO with related molecules, the NCO⁻ ligand was found to be nitrogen bonding to the strontium atom. The Sr-N bond length was estimated to be 2.26 A in the ground state. The rotational analysis of the 0-0 band of the A²E₁/₂ - X²A₁ transition of the SrOCH₃ free radical has been carried out by laser excitation spectroscopy. The SrOCH₃ molecule was found to have C₃ᵥ symmetry with a Sr-O bond length of 2.12 A. There was no evidence of a Jahn-Teller effect in the A²E state. This work is the first high-resolution analysis of a metal alkoxide molecule. The rotationally cool (30 K) spectrum of the 0-0 vibrational band of the A²Δ - X²Π electronic transition for the diatomic free radical CCl was recorded using a Fourier transform spectrometer. The first rotational lines of the six strongest branches were observed, and transitions in three other branches were also detected. The CCl radical was produced in a corona-excited supersonic expansion source.

12

Álvarez, Ruiz Jesús. "Synchrotron radiation induced fluorescence spectroscopy of gas phase molecules." Doctoral thesis, KTH, Physics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-43.

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A new experimental set-up for gas phase fluorescence studies using synchrotron radiation has been designed and constructed to perform simultaneously total and dispersed fluorescence measurements.

Neutral photodissociation of CO has been investigated after excitation with 19-26 eV photons. Fluorescence from 3p 3P, 3p 3S and 3p 1D excited states in carbon was recorded and interpreted by ab initio calculations. The population and dissociation of states belonging to the C and D Rydberg series in CO seem to explain the production of the observed triplet states but not the 3p 1D state.

Neutral photodissociation of NO is reported in the 17-26 eV energy range. No known molecular states can account for the collected data. New information regarding the precursor states of the observed neutral dissociation is provided by ab initio calculations.

Autoionization of superexcited states in molecular nitrogen is evidenced by strong deviations of the Franck-Condon ratio in the fluorescence of the N2+ B state. Ab initio calculations predict the existence of autoionizing-excited states that may account for some of the observed structures in the 20-46 eV energy range.

Selective molecular fluorescence from the npó1Óu+ and npð 1Ðu (n=3-7) Rydberg levels to the E,F 1Óg+ state in H2 was recorded and rotationally analyzed. Vibrational levels of the E,F 1Óg+ state (vEF =0,1,3,6-10) are determined. The predissociation of npð 1Ð+ levels is observed in agreement with the literature.

Fragmentation of SF6 was investigated after excitation with 25–80 eV photons. Dispersed fluorescence measurements reveal the emission of S, S+, F and F+ excited atoms. These fragments are produced after single, double and triple excitations as well as direct ionizations and shake-ups in SF6.

Photoabsorption and fluorescence yield have been measured in SF5CF3 using 10-30eV photons. The photoabsorption spectrum can be explained in terms of its similarities to those of the SF6 and CF4 molecules. The dispersed and un-dispersed fluorescence resemble those of the CF3X family. Several features suggest the migration of an F atom across the S-C bond that fragments the molecule producing excited CF4.

Doubly excited states of H2 have been investigated in the range of 26-60 eV by monitoring Balmer á emission. The experimental data show the already known emission correlated with the fragmentation of the Q1 and Q2 states, and new features which could be attributed to dissociative photoionization and higher lying doubly excited states Qn (n>2) of the hydrogen molecule

13

Cockett, Martin Charles Roy. "Some studies in gas-phase photoelectron and chemielectron spectroscopy." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255760.

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14

Haggerston, Darren. "Some studies in the gas phase using photoelectron spectroscopy." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262155.

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15

Cooper, Graham Alastair. "Spectroscopy and imaging of gas-phase transition metal clusters." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:9db3727c-4246-4d39-95b3-83936265dfad.

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The field of transition metal clusters has proven to be fertile ground for study in recent years due to their interesting properties and reactivity. In this thesis, Velocity Map Imaging (VMI) has been used alongside spectroscopic techniques to study a range of diatomic metal-containing molecules which have relevance to cluster chemistry. The photodissociation of Ag-RG complexes (RG = Ar, Kr, Xe), as well as AgO, have been studied in the 29900-31700 cm⁻¹1 spectral region using VMI. The electronic states of the fragments produced have been assigned in each case and new values for the dissociation energies determined. These are presented as an update to the most recent experimental values for each molecule, about which doubts have been expressed. VMI has also been used to study the photodissociation dynamics of isotopically-selected 98MoO and 52CrO in multiple spectral regions. Assignments have been proposed for the processes generating the observed features, and values for the dissociation energies of these species determined which are consistent with literature values from other, older experimental techniques, or indirect measurements. Finally, a comparison has been made of different image reconstruction algorithms in order to determine which is best suited to analysing the data recorded in our group. The experimental data from the rest of this thesis have been reanalysed using various approaches, and it is demonstrated that recently-developed maximum entropy programs produce better results than the onion peeling algorithm previously used.

16

Baran, Stuart George. "Gas-phase detection methods using diode lasers." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:43e8ec07-9e1a-4060-bc8b-be75c8565600.

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Diode lasers are a convenient and economical source of near-infrared radiation, which may usefully be applied to a host of diﬀerent sensitive detection methods; this thesis presents novel extensions of these methods, making use of the favourable characteristics of this type of light source. The ﬁrst part of this thesis details the development of an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) apparatus, including the development of the optical system, the sample handling, and the electronics for feedback phase control. A preliminary demonstration of the system is reported, presenting the detection of atmospheric water absorptions close to 1596 nm. Optimisation and application of the OF-CEAS spectrometer are then demonstrated, after which the spectrometer is applied to the sensitive detection of carbon dioxide absorptions suitable as a diagnostic aid in identifying Heliobacter pylori infection. A time-normalised α-min value of 5.8 × 10⁻⁹ cm⁻¹s^1/2 was measured for these spectra. Further optimisation of the system leads to an ultimate detection sensitivity of 1.42 × 10⁻⁹ cm⁻¹s^1/2, measured on absorption transitions in acetylene close to 1532 nm. In order further to characterise the performance of the OF-CEAS system, analogous experiments are presented using the OF-CEAS setup and a standard diode-laser cavity-enhanced absorption spectroscopy (CEAS) apparatus. Detection is carried out on the P(6) line of the ν₁ + ν₃ vibrational band of the mixed isotopologue of acetylene, ¹²-C¹³-CH₂. Direct comparison is made between the sensitivities of the two methods, and in light of this the suitability of each technique for detection in diﬀerent environments is considered. The well-characterised and consistent frequency scale which is inherent to the OF-CEAS technique is then applied to a line shape analysis for the presented absorption spectra. Pressure-broadening coeﬃcients are determined for selected absorptions in the ν₁ + ν₃ band of acetylene. In spite of the low resolution associated with this technique, this accurate frequency scaling allows observation of subtle line shape eﬀects such as Dicke collisional narrowing using the data presented in Chapter 3 for the R(60) line in the 3ν₁ + ν₃ vibrational band of CO₂. These eﬀects are quantiﬁed through use of a Galatry ﬁt to each absorption spectrum. The statistical signiﬁcance associated with the use of such a model, and the physical meaning of the results, are examined and discussed. An alternative strategy for increasing the sensitivity of a diode-laser-based gas monitoring technique lies in moving detection to the mid-infrared region, where the absorption cross-sections are generally larger. With this motivation, diﬀerence frequency generation is presented, to produce radiation close to 3.5 µm which is then applied to a series of diﬀerent enhanced spectroscopy techniques. The optimal sensitivity, of 32 ppb NO2 at 45 Torr total sample pressure, was achieved using wavelength modulation spectroscopy. The diﬀerent techniques are compared and possible improvements to them are put forward. Finally, proof-of-principle work is presented seeking to combine the enhanced circulating power associated with the optical-feedback-locked techniques and non-linear optical techniques to move detection to a more favourable spectral region. Light close to 429 nm is generated by second harmonic generation in a crystal of potassium niobate, with resonance-enhancement aﬀorded by a feedback V-cavity of the sort employed in OF-CEAS. The potential of such a system for diode-laser-based generation of blue and ultraviolet light is demonstrated and discussed, along with improvements that might be implemented to increase the eﬃciency of the system.

17

Newnham, David A. "High vibrational overtone spectroscopy." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278081.

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18

Liu, Zhuan. "Infrared diode laser absorption spectroscopy of gas phase molecular ions." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627231.

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19

Knox, David Andrew. "High resolution gas phase spectroscopy at solid/solid interfacial regions." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/high-resolution-gas-phase-spectroscopy-at-solid--solid-interfacial-regions(b5dfd0d0-7c6a-4b50-ad78-39c10c33b3ac).html.

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Understanding the behaviour of polymers which are located in the presence of nuclear materials is important in order to predict the lifespan of the materials. Artificial ageing experiments are undertaken at elevated temperatures to infer how the materials may age. This study was concerned with the monitoring of trace gases (H2O, CO2, CO and acetic acid) within a materials ageing vessel which contained ethylene-vinyl acetate (EVA) polymer and uranium in order to deduce the rate of polymer degradation and/or uptake of the gases by uranium. A novel circular multi-reflective (CMR) cell was designed, developed and deployed in situ in order to extend the optical pathlength within the vessel to improve detection limits of the trace gases. One cell was located at the 6 millimetre solid/solid interfacial region between cylindrical coupons of the EVA polymer and uranium, to enable representative sampling in proximity to where the gases were evolved, adsorbed or reacted. The unique planar star-like beam profile of the CMR cell was crucial in enabling detection within this narrow interfacial region. A second CMR cell was incorporated within the vessel headspace, above the two material coupons, to address a specific research problem which aimed to ascertain whether differences in the gaseous composition existed between the two regions, which would indicate poor gas mixing. Two spectroscopic techniques were employed in conjunction with the CMR cells to monitor the trace gases: these comprised broadband absorption spectroscopy (BBAS) and tunable diode laser absorption spectroscopy (TDLAS). Near-infrared (IR) radiation sources, in the form of diode lasers, a superluminescent light emitting diode (SLED) and supercontinuum (SC) source were utilised in BBAS experiments. TDLAS was used for the detection of CO2, CO and H2O, whilst BBAS was used for the detection of acetic acid, and other potential unknown species. The requirement for using near-IR radiation was a consequence of using flexible silica-based optical fibres to remotely monitor the vessel which was located within a temperature controlled chamber. As a result, this was the first demonstration of CMR cells being used in conjunction with near-IR radiation sources. An optical pathlength of 69 cm was achieved within the materials ageing vessel, which led to the following limits of detection at 75 °C, 150 Torr with a 10 second averaging time: H2O = 3 ppm; acetic acid = 157 ppm; CO2 = 596 ppm and CO = 37500 ppm. Manufacturing issues with the cell optics, coupled with monitoring weak ro-vibrational absorption features led to considerably higher limits of detection than expected. The CMR spectroscopic system was used successfully to observe the outgassing trend of partially cured EVA polymer, which was shown to depend on cure time. A key finding of this research, however, was the observation of a difference between the interfacial gaseous composition versus the headspace gas in a system that contained both a source and sink material (i.e. one that evolved, and one that adsorbed gases). This was only made possible by using the CMR spectroscopic system. This observation was also supported by a computational fluid dynamic (CFD) model.

20

Morse, Jennifer Marie. "Electronic Effects of Solvation: A Comparison of Gas-Phase and Condensed-Phase Photoelectron Spectroscopy." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194130.

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The research presented in this dissertation focuses on the changes to the electronic structures of metal diphosphine and paddlewheel molecules due to different environments, especially intermolecular interactions present in the condensed phase. These intermolecular interactions, measured by photoelectron spectroscopy, represent important aspects of solvation, and an experimental measure of the interactions provides tests for modeling solvent effects. The condensed-phase molecular environment, in the form of thin films on a gold substrate, acts as an effective system to probe the electronic relaxation component of solvent effects by comparing the ionization energies of a molecule in the gas and condensed phase.The challenges of preparing thin films appropriate for study by condensed-phase photoelectron spectroscopy, without appreciable ionization broadening or substrate effects, and the development of a method for calibrating the resulting spectra to the vacuum level have been addressed. This method of calibration has been critical to allow for accurate comparisons of gas-phase and surface photoelectron data that had not been possible previously.The gas-phase and condensed-phase electronic structures of M(CO)4(P-P) (M=Mo, W; P-P=dmpe, dppe) and Mo2(O2CR)4 (R=Me, Ph) have been explored to probe the relative donor strength of methyl- and phenyl-substituted ligands in different environments. A reversal in the relative donor strengths of dmpe and dppe is observed, where dppe is stronger in the gas phase, and dmpe is stronger in the condensed phase; conversely, O2CPh- is a better donor than O2CMe- in both phases. The condensed-phase ionizations are destabilized relative to the gas-phase ionizations for all molecules due to the additional electron relaxation in the solvent environments which stabilizes the positive ion state in the condensed phase. The observed shift of the ionization energies is larger for the methyl-substituted molecules as compared to the phenyl-substituted molecules. Density functional calculations are in agreement with the experimental results and correctly predict the trend in the relative ionization energies of these molecules.The results of these studies indicate that intermolecular interactions, which are accounted for reasonably well by implicit and explicit solvation models, have a greater affect on the electronic structure of the smaller methyl-substituted molecules as compared to the larger phenyl-substituted molecules.

21

Cramb, David Thomas. "Molecular spectroscopy of ionic and neutral species in the gas phase." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30664.

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This thesis details the analyses of high resolution visible, infrared, and microwave spectra of gas phase ionic and neutral molecules. The visible and infrared spectra of several ions were measured using velocity modulation spectrometers developed in the present work. In each case the ions were generated in an electric discharge plasma. The microwave spectrum of vinyl iodide, CH₂=CHI, has been extensively measured and analysed. Visible Spectroscopy using Velocity Modulation: The (6,1) and (13,6) vibrational bands of the A²IIu — X²Σg⁺ electronic transition of N₂⁺ have been recorded in absorption at Doppler limited resolution. The rotational fine structure was fitted by least squares to standard expressions. The rotational and translational temperatures have been measured and indicate an equilibrium between translational and rotational motion in the He/N₂ plasma. Infrared Spectroscopy using Velocity Modulation: The infrared spectra of HCO⁺, H₃⁺ , HeD⁺, and N₂⁺ have been observed. Two previously unmeasured lines of the v₃ band of HCO⁺ and several previously measured lines of the v₂ band of H₃⁺ were used to adjust the spectrometer for maximum sensitivity. A new line in the rotational fine structure of the v = 1 ← 0 band of HeD⁺ was analysed using standard expressions. The rotational fine structure of the (2,5) vibrational band of the A²IIu — X²Σg⁺ electronic transition of N₂⁺ has been recorded and analysed in the region 2125 - 2205 cm⁻¹. Using the vibrational origin, T₂,₅ , obtained from this analysis combined with the origins, T₆,₁ and T₁₃,₆, obtained from the analyses of the visible spectra of N₂⁺ , it was possible to determine third order equilibrium vibrational coefficients for both the X²Σg⁺ and A²IIu states. Microwave Spectroscopy: The microwave spectrum of vinyl iodide, in its ground and first excited vibrational states, has been measured in the frequency range 20 - 108 GHz. The spectrum contains strong a-type transitions and very weak b-type transitions; all contain ¹²⁷I quadrupole hyperfine structure, with several large perturbations. A procedure specially devised for analysis of such spectra, which takes advantage of the perturbations, was applied to produce accurate values of constants that are otherwise unobtainable, and have permitted assignment of some b-type transitions. Also, as a result of this procedure, it was possible to measure both components of the dipole moment with relative ease. The centrifugal distortion constants and inertial defects have been compared with those calculated from a published harmonic force field, modified for the out-of-plane vibrations. A partial structure has been obtained.
Science, Faculty of
Chemistry, Department of
Graduate

22

Forthomme, Damien. "High Resolution Laser Spectroscopy Of Selected Molecules In The Gas Phase." Thesis, Fredericton: University of New Brunswick, 2011. http://hdl.handle.net/1882/35387.

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23

Ali, Sahangir. "Gas phase vacuum-ultraviolet (vuv) spectroscopy of small halogenated polyatomic molecules." Thesis, University of Birmingham, 2007. http://etheses.bham.ac.uk//id/eprint/897/.

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The work carried out in this thesis is concerned with photoexcitation of small and halogenated molecules in the gas phase with vacuum-ultraviolet (VUV) radiation. For all the experiments described in this thesis, the source of radiation was from tuneable VUV radiation from a synchrotron source. The majority of the experiments used the UK national source located at Daresbury Cheshire. Fluorescence spectra were taken using the newly commissioned Wadsworth monochromator on beamline 3.1 of the Daresbury synchrotron radiation source. Dispersed florescence spectra were taken using a newly developed fluorescence apparatus incorporating a multi-channel CCD detection system. One of the objectives of this thesis is to compare the sensitivity and resolution of this new system with that of an apparatus used at the BESSY 1 synchrotron source in the 1990s. Many of the molecules studied here were chosen because previous data recorded at BESSY 1 were available for this comparison. Molecules studied include the MCl$_4$ series (M = C, Si and Ge) where both the VUV photoabsorption and fluorescence spectra were recorded. A new analysis of the absorption spectra is presented. Emissions are observed in MCl$_2$, MCl and the parent ion of SiCl$_4^+$ and GeCl$_4^+$. The CF$_3$X series (X = H, F, Cl, Br, I and SF$_5$) where the fluorescence spectra and some photoabsorption spectra were recorded. Emissions are observed in CF, CF$_2$, CF$_3$ and parent ion CF$_4^+$, CF$_3$H$^+$. Undispersed and dispersed fluorescence spectra of BX$_3$ (X = F, Cl and Br) were also recorded. Emission is now observed in BX$_2$, BX and parent ion BX$_3^+$. Finally the fluorescence spectra of PX$_3$ (X = F, Cl and Br) were recorded and are presented here. Emissions are observed in PX$_2$, PX and parent ion PX$_3^+$.

24

Borkar, Sampada N. "Very accurate gas-phase thermochemistry through photoelectron photoion coincidence (PEPICO) spectroscopy." Scholarly Commons, 2013. https://scholarlycommons.pacific.edu/uop_etds/144.

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Five projects are presented here that use Photoelectron Photoion Coincidence (PEPICO) Spectroscopy to determine high-accuracy thermochemical data on small and intermediate size molecules and radicals that are relevant in modeling combustion and atmospheric processes. Some of the experiments were carried out on the laboratory-based Threshold PEPICO (TPEPICO) apparatus which has the advantage of having a low-temperature inlet system and unlimited measurement time, while most of the projects involved the use of the Imaging PEPICO (iPEPICO) apparatus at the Swiss Light Source, which is capable to determine ionic dissociation energies to sub-kJ/mol accuracy. The iPEPICO on the synchrotron beamline was also useful where measurements required energies in excess of 14 eV. The modeling framework of PEPICO is based on the RRKM statistical theory of dissociation kinetics and statistical energy distributions and models complex dissociation pathways to extract both kinetics and thermochemical data from the experiment. In the first project, we measured the onsets of Br- and I-loss reactions for C 2 H 5 Br and C 2 H 5 I using TPEPICO, respectively. The heats of formations of the two molecules are related through the ethyl cation, which was used in their determination. The second project involved measuring Cl-loss from four S i O j Cl k compounds viz. SCl 2 , S 2 Cl 2 , SOCl 2 , and SO 2 Cl 2 to obtain reliable thermochemistry. The second Cl-loss from S 2 Cl 2 + and SOCl 2 + helped us conclude that assuming three-dimensional translational degrees of freedom yields a more reliable statistical model of product-energy distributions. The third project investigated methanol and its isotopologues to explore the dissociation pathways through the H/D-losses. The 0 K appearance energies were used to determine the accurate heat of formation of CH 2 OH and the proton affinity of formaldehyde. The fourth project explores the dissociation pathways of cis -1-bromopropene, trans -1-bromopropene, 2-bromopropene, 3-bromopropene and bromocyclopropane to find that except for 2-bromopropene, all other isomers dissociate into the allyl cation. To derive accurate thermochemical information on the neutral precursors, a mixed theoretical and experimental thermochemical network was used to determine their 0 K heats of formation. The last project involves measurements on dimethyl disulfide (DMDS) and dimethyl diselenide, which are the simplest models that can be used to study disulfide and diselenide linkages. There are several discrepancies in the thermochemistry of DMDS, whereas ours is the first experimental attempt to study the ionic thermochemistry of dimethyl diselenide experimentally.

25

Villano, Stephanie M. "Gas-phase negative ion chemistry: Photoelectron spectroscopy, reactivity, and thermochemical studies." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337158.

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26

Bopegedera, A. M. Ranjika Priyadarshi. "Dye laser and diode laser spectroscopy of gas phase free radicals." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184695.

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The gaseous free radicals, alkaline-earth metal monoalkylamides, monoacetylides, monoformamidates and monopyrrolidates, consisting of a metal atom (Ca or Sr) bonded to a single ligand, were synthesized in a Broida oven. The electronic and vibrational structures of these molecules were studied by low-resolution laser spectroscopy techniques. These inorganic molecules are ionic, well represented by the structure M⁺L⁻ (M = Ca, Sr: L = ligand). Three electronic transitions were identified for the metal monoalkylamides and the metal monoformamidates. The formamidate anion bonds to the metal in a bidentate fashion through the oxygen and nitrogen atoms. Two electronic transitions were observed for the metal monopyrrolidates. The pyrrolide anion ring bonds to the metal to provide these "open-faced sandwich" type molecules with pseudo-C₅ᵥ symmetry. For the metal monoacetylide molecules, only one electronic transition (Ā²Π-Ẋ²Σ⁺) was observed. Several vibrational frequencies were determined for these inorganic molecules from the low-resolution spectra. The Ā²Π-Ẋ²Σ⁺ transition of the calcium monoacetylide molecule was rotationally analyzed at high-resolution using the filtered laser excitation spectoscopy technique. The rotational line positions were fitted to a ²Π-²Σ⁺ Hamiltonian to obtain several rotational constants. The calcium-carbon bond length in CaCCH was calculated for the ground (2.248 Å) and excited (2.200 Å) electronic states. The vibration-rotation spectra of the gaseous bismuth hydride and bismuth deuteride molecules were recorded, using a diode laser system. The 1-0 fundamental band and several hot bands with Δv-1 were rotationally analyzed. The rotational line positions were fitted first, to a Dunham energy expression and then to a ³Σ⁻ Hamiltonian, to obtain ground state rotational constants. The bismuth-hydrogen (deuterium) bond distance was calculated to be 1.809 Å (1.807 Å).

27

Haverd, Vanessa. "Time resolved Fourier transform infrared emission studies of gas phase kinetics and dynamics." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270047.

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28

Dookwah-Roberts, Venus Maria Christina. "Spectroscopy and Kinetics of Weakly Bound Gas-Phase Adducts of Atmospheric Interest." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24743.

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A number of weakly bound adducts play important roles in atmospheric chemistry, such as DMS OH and CS2 OH. The work comprising this dissertation involves kinetic and spectroscopic studies of adducts formed between halogen atoms and the important atmospheric trace gases CS2, CH3SCH3 (DMS), CH3I, and C2H5I. The results reported in these studies are useful for developing an understanding of the reactivity of these species and for testing the ability of electronic structure theory and reaction rate theory to predict or rationalize any observed trends. Oxidative pathways of both alkyl halides and sulfur compounds, especially DMS, are of atmospheric interest based on the roles of these species in affecting the oxidizing capacity of the troposphere and in the formation of new particles which impact the Earth s radiation budget and climate variability. The experimental approach employed laser flash photolysis (LFP) coupled with time resolved UV-visible absorption spectroscopy (TRUVVAS) to investigate the spectroscopy and kinetics of the gas phase adducts: SCS Cl, CH3I Cl, C2H5I Cl, (CH3)2S Br, and (CH3)2S I.

29

Zimmermann, Nina Tamara [Verfasser]. "Manganese oxide cluster : Gas phase reactions and IR spectroscopy / Nina Tamara Zimmermann." Ulm : Universität Ulm, 2021. http://d-nb.info/1231916494/34.

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30

Li, Kexin. "GAS PHASE MICROWAVE SPECTROSCOPY AND INSTRUMENT DEVELOPMENT ON A DOUBLE RESONANCE EXPERIMENT." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/618749.

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High resolution rotational spectroscopy is a powerful technique to identify and characterize the accurate structures of volatile, polar and relatively rigid molecules. The first Pulse Beam Fourier transform microwave (FTMW) spectroscopy was constructed by Flygare and Balle in 1981 and provided great improvements in sensitivity and resolution in molecular spectroscopy. The double resonance FTMW spectrometer uses a new method to probe the rotational transitions that share a common quantum state. The linkage information can be used to assign weak transitions. We want to present the current work on hardware and software updates on the instrumentation. The theoretical models such as density functional theory and ab-initio method are used to provide initial estimates for microwave measurement parameters and to help guide transition assignments.

31

Weichmann, Marissa L., Xiaowei Song, Matias R. Fagiani, Sreekanta Debnath, Sandy Gewinner, Wieland Schöllkopf, Daniel M. Neumark, and Knut Roger Asmis. "Gas phase vibrational spectroscopy of cold (TiO2)−n (n = 3–8) clusters." AIP Publishing, 2016. https://ul.qucosa.de/id/qucosa%3A21255.

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We report infrared photodissociation (IRPD) spectra for the D2-tagged titanium oxide cluster anions (TiO2)−n with n = 3–8 in the spectral region from 450 to 1200 cm−1. The IRPD spectra are interpreted with the aid of harmonic spectra from BP86/6-311+G* density functional theory calculations of energetically low-lying isomers. We conclusively assign the IRPD spectra of the n = 3 and n = 6 clusters to global minimum energy structures with Cs and C2 symmetry, respectively. The vibrational spectra of the n = 4 and n = 7 clusters can be attributed to contributions of at most two low-lying structures. While our calculations indicate that the n = 5 and n = 8 clusters have many more low-lying isomers than the other clusters, the dominant contributions to their spectra can be assigned to the lowest energy structures. Through comparison between the calculated and experimental spectra, we can draw conclusions about the size-dependent evolution of the properties of (TiO2)−n clusters, and on their potential utility as model systems for catalysis on a bulk TiO2 surface.

32

Dookwah-Roberts, Venus Maria Christina. "Spectroscopy and kinetics of weakly bound gas-phase ddducts of atmospheric interest." Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24743.

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Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2008.
Committee Chair: Wine, Paul; Committee Member: Huey, Greg; Committee Member: Nenes, Athanasios; Committee Member: Weber, Rodney; Committee Member: Whetten, Robert.

33

Aliwell, Simon Richard. "Measurement of atmospheric trace gases by absorption spectroscopy." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388668.

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34

Briggs, Ronald D. "High-resolution nonlinear laser wave-mixing spectroscopy for gas-phase environmental and atmospheric studies /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3112972.

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35

Daly, Adam Michael. "Gas Phase Structures and Molecular Constants of Dimers and Molecules Determined using Microwave Spectroscopy." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195595.

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Gas phase structures and other molecular parameters have been investigated for several molecules and dimers using pulsed beam Fourier Transform Microwave Spectroscopy. An automated control system has been designed and implemented for the microwave spectrometer that has allowed a systematic observation of the microwave spectrum for many molecules. The theoretical models that are available to the gas phase structural chemist, density functional theory and ab-initio methods, are described with detailed comparisons to experimental results. Experimental data was generated for systems involving hydrogen bonded dimers, organic molecules, inorganic molecules and organometallic molecules. Rotational constants and quadrupole coupling constants were determined using the microwave spectra. This data and isotopic investigations have been used to determine key structural parameters and molecular properties.

36

Ashman, A. S. "Laser spectroscopy of molecular ions in an Ion Cyclotron Resonance apparatus." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234408.

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37

Gause, Oliver [Verfasser]. "Femtosecond spectroscopy and coherent control on flavins in the gas phase / Oliver Gause." Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1027151558/34.

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38

Medvecz, Patrick J. "Spectroscopic evaluation of the gas phase above a burning black liquor char bed." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/5759.

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39

Hansford, Graeme Mark. "Diode laser infrared spectroscopy of jet-cooled polyatomic molecules." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321031.

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40

Rius, i. Riu Jaume. "Gas phase molecular relaxation probed by synchrotron radiation experiments." Doctoral thesis, KTH, Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3411.

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This thesis presents experimental studies of gas phasemolecular relaxation after excitation with synchrotron photonsin the 15-35 eV and in the 70-350 eV regions.

In the 15-35 eV region, molecular relaxation by neutraldissociation processes and non

Franck-Condon effects in N2 and O2 molecules have beenstudied by means of dispersed fluorescence and photoelectronspectroscopy experimental techniques, respectively. From thedispersed fluorescence data, excitation functions for themeasured atomic fluorescence spectra have been obtained. Fromthe recorded photoelectron spectra vibrational branching ratioshave been produced. The results obtained reveal that Rydbergseries and singly and doubly excited valence states of theappropriate symmetry energetically accessible in the studiedregion and interactions between themaccount for most of theobserved effects in these two type of experiments.

In the 70-350 eV range, molecular relaxation processesresulting in fragmentation of CD4 and SF6 after absorption ofsynchrotron light have been studied by energy resolved electronion coincidence technique using a multicoincidence experimentalstation developed by our group during the last five years forsuch type of experiments. The coincidence measurements yieldedmass spectra from which information about the kinematics of thedetected fragments has been deduced by means of Monte Carlosimulations of the experimental peak shapes. The obtainedresults show completely different dissociation patternsdepending on the molecular electronic states studied. Thesepatterns reflect the bonding properties of the excited orbitalsand they permit the description and in some cases theidentification of the different molecular relaxation pathwaysobserved. The achievements presented in this thesis exemplifythe potential of the multicoincidence station used in thereported experiments.

41

Esposito, Anthony Paul. "Resonance Raman studies of halooxide photochemistry in the gas and condensed phase /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/8616.

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42

Raja, Ibrahim Raja Kamarulzaman Kamarulzaman. "Mid-infrared diagnostics of the gas phase in non-thermal plasma applications." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/midinfrared-diagnostics-of-the-gasphase-in-nonthermal-plasmaapplications(3b684a12-78fa-4d9b-94d2-0f066b7a828e).html.

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This thesis focuses on the utilisation of mid-infrared techniques in technological atmospheric pressure, non-thermal plasma (NTP) diagnostics. Two mid-infrared techniques were demonstrated in this work namely laser absorption and Fourier transform infrared (FTIR) spectroscopy. The performance of external-cavity quantum cascade laser (EC-QCL), a relatively new laser type with broad tuning capability was also demonstrated as potential diagnostics tool for technological NTP applications. A dual plate dielectric barrier discharge (DBD) and a packed-bed NTP reactor were designed and fabricated to perform plasma process. Quantitative analysis of the laser absorption and FTIR spectroscopy techniques for gas detection were validated by using standard gas samples. Real-time CO monitoring by means of in-situ laser absorption spectroscopy measurements were performed for gas phase diagnostics in the decomposition of TEOS by means of plasma-enhanced chemical vapour deposition (PE-CVD) and in CO2 reforming of CH4 by means of NTP. In-line FTIR measurements simultaneously recorded the gas spectrum at the exhaust of the plasma reactors. Information from both measurements was found to provide useful information on the plasma processes and chemistry for the NTP applications. Finally, wavelength stability and linearity performance of a broad tuning range EC-QCL were evaluated by using the Allan variance technique. (LOD) at SNR = 1 was estimated to be ~ 2 ppm, achieved under atmospheric pressure, at the room temperature, and a path length of 41 cm for NO detection produced from the decomposition of dichloromethane (DCM) by means of NTP.

43

Schubert, Franziska [Verfasser]. "Conformational equilibria and spectroscopy of gas-phase homologous peptides from first principles / Franziska Schubert." Berlin : Freie Universität Berlin, 2014. http://d-nb.info/106294917X/34.

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44

Butcher, V. A. "Studies of some reactive intermediates in the gas-phase by ultra-violet photoelectron spectroscopy." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381210.

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45

Qian, Haibo. "Diode laser spectroscopy of free radicals and other transient molecules in the gas phase." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627118.

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46

Smith, Zachary Michael. "Computational Investigations of the Structure and Spectroscopy of Small Biomolecules in the Gas Phase." W&M ScholarWorks, 2018. https://scholarworks.wm.edu/etd/1550153898.

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Small biomolecule systems were interrogated using infrared multiple photon dissociation (IRMPD) action spectroscopy and corresponding quantum chemical calculations with a particular focus on peptide fragmentation and protonation site preference. b2+ and b3+ fragment ions with a terminal lysine homolog residue were investigated using IRMPD in the fingerprint region (1000 cm-1 – 2000 cm-1) and a variety of computational methods. We present the first spectroscopic confirmation of b-ion formation with a lactam structure. Infrared spectra for b2+ fragment system indicate the presence of a mixture of structures, though final determination will require further investigation. The b3+ fragment ion infrared spectra show strong support for the presence of a predominantly lactam structure. Extensive computational research in this system suggests the B3LYP method to be the most computationally efficient density functional theory method for spectral predictions. However, the inclusion of p-polarization into the basis set yielded inconclusive results and should be investigated further.

47

Culberson, Lori. "Molecular Electronic Structure via Photoelectron Imaging Spectroscopy." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/301677.

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This dissertation explores the use of photoelectron imaging spectrometry to probe the molecular electronic structure of various chemical systems, with an emphasis on photoelectron angular distributions. Experimental ion generation, mass selection, laser photodetachment, and photoelectron ion imaging were all done in a photoelectron imaging spectrometer described in detail. Results from simplistic systems, OH- and CH-, are used to illustrate the general and fundamental capabilities of imaging spectroscopy and angular distributions. This illustration is then expanded when both qualitative and quantitative analyses of photoelectron angular distributions are used to aid in the understanding of the electronic structure of several heterocyclic aromatic systems. First a qualitative analysis aids in the exploration of the electronic structure of thiophenide, C₄H₃S⁻, and furanide, C₄H₃O⁻. Ground and excited C₄H₃S and C₄H₃O radical states are observed, and bond dissociation energies are defined. Next, a new model used to qualitatively analyze photoelectron angular distributions resulting from mixed s - p hybrid states is presented and applied to detachment from pyridinide, C₅H₄N⁻; as a benchmark system. Before further exploring this model, the synthesis of several deuterated heterocyclic compounds is presented in order to determine the experimentally produced systems in our experimental setup. The electronic structure of the resultant molecules oxazolide, C₃H₂NO⁻, and thiazolide, C₃H₂NS⁻; are then investigated. Using this new qualitative model, the mixed s - p states model, to evaluate the angular distributions of the systems, the hybridization of the anion molecular orbitals is probed. Comparison of the photoelectron angular distributions that are modeled for each heterocyclic aromatic system yields several trends relating aromatic stabilization, molecular hybridization, and bond dissociation energies. A new qualitative model is then presented to evaluate photoelectron angular distributions resulting from mixed p - d states and applied to detachment from NO⁻. Finally, new ideas and directions are proposed.

48

Hanni, M. (Matti). "Static and dynamic NMR properties of gas-phase xenon." Doctoral thesis, University of Oulu, 2011. http://urn.fi/urn:isbn:9789514294570.

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Abstract This thesis presents computational studies of both the static and dynamic parameters of the nuclear magnetic resonance (NMR) spectroscopy of gaseous xenon. First, state-of-the-art static magnetic resonance parameters are computed in small xenon clusters by using methods of quantum chemistry, and second, time-dependent relaxation phenomena are investigated via molecular dynamics simulations at different experimental conditions. Based on the underlying quantum and classical mechanics concepts, computational methods represent a procedure complementary to experiments for investigating the properties of atoms, molecules, clusters and solids. Static NMR spectral parameters, chemical shift, shielding anisotropy and asymmetry parameter, nuclear quadrupole coupling, and spin-rotation coupling, are calculated using different electronic structure methods ranging from the uncorrelated Hartree-Fock method to correlated second-order Møller-Plesset many-body perturbation, complete/restricted active space multiconfiguration self-consistent field, and to coupled-cluster approaches. The bond length dependence of these properties is investigated in the xenon dimer (Xe2). A well-characterized property in experimental NMR, the second virial coefficient of nuclear shielding, is theoretically calculated by a variety of methods and convincingly verified against experimental findings. Here, it is mandatory to include effects from special relativity as well as electron correlation. As a side result, a purely theoretical potential energy curve for Xe2, comparable to best experimental ones, is calculated. A pairwise additive scheme is established to approximate the NMR properties in differently coordinated sites of xenon clusters Xen (n = 2 - 12). Especially the pairwise additive chemical shift values are found to be in close agreement with quantum-chemical results and only a small scaling factor close to unity is needed for the correct behavior. Finally, a dynamical magnetic resonance property, the experimental nuclear spin-lattice relaxation rate R1 of monoatomic Xe gas due to the chemical shift anisotropy (CSA) mechanism is validated from first principles. This approach is based on molecular dynamics simulations over a large range of temperatures and densities, combined with the pairwise additive approximation for the shielding tensor. Therein, the shielding time correlation function is seen to reflect the characteristic time scales related to both interatomic collisions and cluster formation. For the first time, the physics of gaseous xenon is detailed in full in the context of CSA relaxation.

49

Kaposta, Eva Cristina. "Gas phase infrared photodissociation spectroscopy mass selected cluster ions strong hydrogen bonds and vanadium oxides /." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=978049314.

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Fagiani, Matias Ruben [Verfasser]. "Cryogenetic ion vibrational spectroscopy of gas-phase clusters : Structure, Anharmonicity and Fluxionality / Matias Ruben Fagiani." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/113162937X/34.

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Дисертації з теми "Terahertz gas phase spectroscopy"

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