Добірка наукової літератури з теми "Laser Induced Molecular Dissociation"

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Статті в журналах з теми "Laser Induced Molecular Dissociation"

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Numico, R., A. Keller, and O. Atabek. "Laser-induced molecular alignment in dissociation dynamics." Physical Review A 52, no. 2 (August 1, 1995): 1298–309. http://dx.doi.org/10.1103/physreva.52.1298.

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Kato, Shuji, Yoshihiro Makide, Takeshi Tominaga, and Kazuo Takeuchi. "Infrared Multiphoton Dissociation of CF3CHClF: Primary Dissociation and Secondary Photolysis." Laser Chemistry 8, no. 2-4 (January 1, 1988): 211–34. http://dx.doi.org/10.1155/lc.8.211.

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The dissociation yield and branching ratio in CO2 laser-induced infrared multiphoton dissociation (IRMPD) of CF3CHClF were investigated by irradiation at 9R(20) 1078.6 cm−1 under an unfocused irradiation geometry (0.75-2.3 J/cm2) and a mildly focused one (1.2-18 J/cm2). By using a Br2-scavenging technique, it was revealed that the primary dissociation of CF3CHClF proceeded mainly via three-centered HCl molecular elimination and C-Cl bond rupture, with minor contributions of C-C bond rupture and HF molecular elimination at higher fluences. The secondary photolysis of the primarily produced species during the laser pulse to yield CF2 and CClF carbenes depended strongly upon the laser fluence.
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3

He, X., O. Atabek, and A. Giusti-Suzor. "Laser-induced resonances in molecular dissociation in intense fields." Physical Review A 38, no. 11 (December 1, 1988): 5586–94. http://dx.doi.org/10.1103/physreva.38.5586.

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4

Akram, M., Raheel Ali, and M. A. Baig. "Laser induced molecular dissociation and ionization of potassium vapour." Optics Communications 136, no. 5-6 (April 1997): 390–94. http://dx.doi.org/10.1016/s0030-4018(96)00713-4.

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Hoang Man, Viet, Nguyen-Thi Van-Oanh, Philippe Derreumaux, Mai Suan Li, Christopher Roland, Celeste Sagui, and Phuong H. Nguyen. "Picosecond infrared laser-induced all-atom nonequilibrium molecular dynamics simulation of dissociation of viruses." Physical Chemistry Chemical Physics 18, no. 17 (2016): 11951–58. http://dx.doi.org/10.1039/c5cp07711g.

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6

Csehi, András, Gábor J. Halász, Lorenz S. Cederbaum, and Ágnes Vibók. "Towards controlling the dissociation probability by light-induced conical intersections." Faraday Discussions 194 (2016): 479–93. http://dx.doi.org/10.1039/c6fd00139d.

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Light-induced conical intersections (LICIs) can be formed both by standing or by running laser waves. The position of a LICI is determined by the laser frequency while the laser intensity controls the strength of the nonadiabatic coupling. Recently, it was shown within the LICI framework that linearly chirped laser pulses have an impact on the dissociation dynamics of the D2+molecule (J. Chem. Phys.,143, 014305, (2015);J. Chem. Phys.,144, 074309, (2016)). In this work we exploit this finding and perform calculations using chirped laser pulses in which the time dependence of the laser frequency is designed so as to force the LICI to move together with the field-free vibrational wave packet as much as possible. Since nonadiabaticity is strongest in the vicinity of the conical intersection, this is the first step towards controlling the dissociation processviathe LICI. Our showcase example is again the D2+molecular ion. To demonstrate the impact of the LICIs on the dynamical properties of diatomics, the total dissociation probabilities and the population of the different vibrational levels after the dissociation process are studied and discussed.
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7

Abeln, B., J. V. Hernández, F. Anis, and B. D. Esry. "Comparison of theoretical analyses of intense-laser-induced molecular dissociation." Journal of Physics B: Atomic, Molecular and Optical Physics 43, no. 15 (July 7, 2010): 155005. http://dx.doi.org/10.1088/0953-4075/43/15/155005.

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Lai, G. D., Y. L. Zhao, S. N. Luo, and J. C. Shi. "Influence of the molecular structure on heterocyclic-ring dissociation kinetics and structural evolution of laser-induced plasmas." Journal of Analytical Atomic Spectrometry 36, no. 8 (2021): 1742–49. http://dx.doi.org/10.1039/d1ja00166c.

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Exploring the influence of the molecular structure on the dissociation kinetics and structural evolution of heterocyclic rings in fs laser-induced plasma based on temporally and spatially resolved measurements.
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Alexander, J. D., C. R. Calvert, R. B. King, O. Kelly, W. A. Bryan, G. R. A. J. Nemeth, W. R. Newell, et al. "Short pulse laser-induced dissociation of vibrationally cold, trapped molecular ions." Journal of Physics B: Atomic, Molecular and Optical Physics 42, no. 15 (July 16, 2009): 154027. http://dx.doi.org/10.1088/0953-4075/42/15/154027.

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Zhang, Wei, Lirong Bao, Kexin Jiang, Anran Shi, Ruiqi Shen, and Yinghua Ye. "Identification and formation mechanism of the transient ion fragments produced in laser-induced dissociation of 1, 1-diamino-2, 2-dinitroethylene." Laser and Particle Beams 36, no. 3 (September 2018): 308–12. http://dx.doi.org/10.1017/s0263034618000290.

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AbstractDetailed knowledge of dissociation behavior and dissociation products is necessary to understand the stability, sensitivity, and the reactive mechanism of explosives under laser initiation. A time-of-flight mass spectrometer was utilized to detect the transient products of 1,1-diamino-2,2-dinitroethylene (FOX-7) produced under 532 nm pulse laser ablation, the possible attribution of intermediate ion fragments were confirmed. The laser fluence threshold for detectable fragments is about 3.6 J/cm2. The peak intensities of main ions (CN, CNO/C2H4N, NO2, C2N2O, HCN, C2NH2, etc.) increase with the increasing of laser fluence, and reach the maximum at 11.5 J/cm2. Moreover, time-depend changes of ion intensity indicate that the type and degree of reactions are different in different periods. According to the molecular structure of FOX-7 and the intermediate ions, the laser-induced dissociation mechanisms were proposed to illustrate the cause of the fragments which might throw some light on the laser initiation of FOX-7.
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Дисертації з теми "Laser Induced Molecular Dissociation"

1

Gaire, Bishwanath. "Imaging of slow dissociation of the laser induced fragmentation of molecular ions." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8852.

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Doctor of Philosophy
Department of Physics
Itzhak Ben-Itzhak
Lasers are being used widely for the study and manipulation of the dynamics of atomic and molecular targets, and advances in laser technology makes it possible to explore new areas of research — for example attosecond physics. In order to probe the fragmentation dynamics of molecular ions, we have developed a coincidence three-dimensional momentum imaging method that allows the kinematically complete study of all fragments except electrons. Recent upgrades to this method allow the measurement of slow dissociation fragments, down to nearly zero velocity, in intense ultrafast laser fields. Evidences for the low energy breakup are presented using the benchmark molecules diatomic H[subscript]2[superscript]+ and polyatomic H[subscript]3[superscript]+ . The low energy fragments in H[subscript]2[superscript]+ dissociation are due to the intriguing zero-photon dissociation phenomenon. This first experimental evidence for the zero-photon dissociation is further supported by sophisticated theoretical treatment. We have explored the laser pulse length, intensity, wavelength, and chirp dependence of zero-photon dissociation of H[subscript]2[superscript]+, and the results are well described by a two-photon process based on stimulated Raman scattering. Similar studies of the slow dissociation of H[subscript]3[superscript]+ reveal that two-body dissociation is dominant over three-body dissociation. The most likely pathways leading to low-energy breakup into H[superscript]++H[subscript]2, in contradiction to the assessments of the channels in at least one previous study, are explored by varying the laser pulse duration and the wavelength. In addition, we have investigated the dissociation and single ionization of N[subscript]2[superscript]+ , and an interesting high energy feature in addition to the low energy has been observed at higher intensities. Such high energy results from the breakup of molecules in excited states are accessible at higher intensities where their potential energy is changing rapidly with the internuclear distance. We have extended the intense field ionization studies to other molecular ions N[subscript]2[superscript]+ , CO[superscript]+, NO[superscript]+, and O[subscript]2[superscript]+ . The dissociative ionization of these molecules follow a general mechanism, a stairstep ionization mechanism. Utilizing the capability of the upgraded experimental method we have measured the non-dissociative and dissociative ionization of CO[superscript]+ using different pulse lengths. The results suggest that dissociative ionization can be manipulated by suppressing some ionization paths.
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2

Ray, Dipanwita. "Photo-electron momentum distribution and electron localization studies from laser-induced atomic and molecular dissociations." Diss., Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/3901.

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Fischer, Andreas [Verfasser], and Robert [Akademischer Betreuer] Moshammer. "Dissociative Photoionization of Molecular Hydrogen - A Joint Experimental and Theoretical Study of the Electron-Electron Correlations induced by XUV Photoionization and Nuclear Dynamics on IR-Laser Dressed Transition States / Andreas Fischer ; Betreuer: Robert Moshammer." Heidelberg : Universitätsbibliothek Heidelberg, 2015. http://d-nb.info/1180301552/34.

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4

Folkerts, Hein Otto. "Molecular dissociation induced by electron transfer to multicharged ions." [S.l. : [Groningen] : s.n.] ; [University Library Groningen] [Host], 1996. http://irs.ub.rug.nl/ppn/14544757X.

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Purcell, S. M. "Laser induced molecular motion in strong nonresonant laser fields." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/19225/.

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The optical dipole force from a singe focussed laser beam was used to study the role of laser-induced molecular alignment on the centre-of-mass motion of carbon disulphide molecules in a molecular beam. The translational, rotational and vibrational temperatures of the carbon disulphide molecules were measured to be 3.4\pm0.2 K, 35\pm10 K and 250\pm14 K respectively. The velocity of the beam was measured to be 542\pm22 m s ^{-1}. Time-of-flight mass spectroscopy was used to measure the acceleration and deceleration of the molecules. Maximum velocity changes of 7.5 m s ^{-1} and 10 m s ^{-1} were recorded for linearly and circularly polarised light respectively. These results showed that the dipole force, \digamma \alpha \bigtriangledown [\alpha_e_f_f(I)I(r)], where \alpha_e_f_f is the effective polarisability and determined through laser-induced alignment, can be modified by changing the laser polarisation. For linearly and circularly polarised light, a 12% difference in effective polarisability was measured to produce a 20% difference in dipole force. The dipole force from a single focussed laser beam produces a molecular optical lens and the downstream density of the molecular focus was probed by measuring the ion signal for both laser polarisations. The focal lengths for linearly and circularly polarised light were found to be separated by \approx 100 \mu m. By altering the laser polarisation from linearly through elliptically to circularly polarised light, the focal length of the molecular optical lens could be smoothly altered over the \approx 100 \mu m focal range. The role of the effective polarisability of each rotational state was also studied numerically. Separate rotational states were found to significantly alter the focal properties of a molecular optical lens. In carbon disulphide, higher rotational states (J > 10), exhibit less molecular alignment and when occupied, the focal length of the molecular optical lens for these states was increased by 60 % compared to the ground state.
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McKendrick, Colin Bruce. "UV laser multiphoton dissociation studies of H2O, NO2 and H2O2." Thesis, University of Edinburgh, 1986. http://hdl.handle.net/1842/12630.

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Zohrabi, Mohammad. "Quantum control of molecular fragmentation in strong laser field." Diss., Kansas State University, 2014. http://hdl.handle.net/2097/18401.

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Анотація:
Doctor of Philosophy
Department of Physics
Itzhak Ben-Itzhak
Present advances in laser technology allow the production of ultrashort (≲5 fs, approaching single cycle at 800 nm), intense tabletop laser pulses. At these high intensities laser-matter interactions cannot be described with perturbation theory since multiphoton processes are involved. This is in contrast to photodissociation by the absorption of a single photon, which is well described by perturbation theory. For example, at high intensities (≳5×10[superscript]13 W/cm[superscript]2) the fragmentation of molecular hydrogen ions has been observed via the absorption of three or more photons. In another example, an intriguing dissociation mechanism has been observed where molecular hydrogen ions seem to fragment by apparently absorbing no photons. This is actually a two photon process, photoabsorption followed by stimulated emission, resulting in low energy fragments. We are interested in exploring these kinds of multiphoton processes. Our research group has studied the dynamics and control of fragmentation induced by strong laser fields in a variety of molecular targets. The main goal is to provide a basic understanding of fragmentation mechanisms and possible control schemes of benchmark systems such as H[subscript]2[superscript]+. This knowledge is further extended to more complex systems like the benchmark H[subscript]3[superscript]+ polyatomic and other molecules. In this dissertation, we report research based on two types of experiments. In the first part, we describe laser-induced fragmentation of molecular ion-beam targets. In the latter part, we discuss the formation of highly-excited neutral fragments from hydrogen molecules using ultrashort laser pulses. In carrying out these experiments, we have also extended experimental techniques beyond their previous capabilities. We have performed a few experiments to advance our understanding of laser-induced fragmentation of molecular-ion beams. For instance, we explored vibrationally resolved spectra of O[subscript]2[superscript]+ dissociation using various wavelengths. We observed a vibrational suppression effect in the dissociation spectra due to the small magnitude of the dipole transition moment, which depends on the photon energy --- a phenomenon known as Cooper minima. By changing the laser wavelength, the Cooper minima shift, a fact that was used to identify the dissociation pathways. In another project, we studied the carrier-envelope phase (CEP) dependences of highly-excited fragments from hydrogen molecules. General CEP theory predicts a CEP dependence in the total dissociation yield due to the interference of dissociation pathways differing by an even net number of photons, and our measurements are consistent with this prediction. Moreover, we were able to extract the difference in the net number of photons involved in the interfering pathways by using a Fourier analysis. In terms of our experimental method, we have implemented a pump-probe style technique on a thin molecular ion-beam target and explored the feasibility of such experiments. The results presented in this work should lead to a better understanding of the dynamics and control in molecular fragmentation induced by intense laser fields.
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Ablikim, Utuq. "Fragmentation of molecular ions in ultrafast laser pulses." Kansas State University, 2015. http://hdl.handle.net/2097/18962.

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Анотація:
Master of Science
Department of Physics
Itzhak Ben-Itzhak
Imaging the interaction of molecular ion beams with ultrafast intense laser fields is a very powerful method to understand the fragmentation dynamics of molecules. Femtosecond laser pulses with different wavelengths and intensities are applied to dissociate and ionize molecular ions, and each resulting fragmentation channel can be studied separately by implementing a coincidence three-dimensional (3D) momentum imaging method. The work presented in this master’s report can be separated into two parts. First, the interaction between molecular ion beams and femtosecond laser pulses, in particular, the dissociation of CO[superscript]+ into C[superscript]++O, is studied. For that purpose, measurements are conducted at different laser intensities and wavelengths to investigate the possible pathways of dissociation into C[superscript]++O. The study reveals that CO[superscript]+ starts to dissociate from the quartet electronic state at low laser intensities. Higher laser intensity measurements, in which a larger number of photons can be absorbed by the molecule, show that the doublet electronic states with deeper potential wells, e.g. A [superscript]2Π, contribute to the dissociation of the molecule. In addition, the three-body fragmentation of CO[subscript]2[superscript]+ into C[superscript]++O[superscript]++O[superscript]+ is studied, and two breakup scenarios are separated using the angle between the sum and difference of the momentum vectors of two O[superscript]+ fragments. In the second part, improvements in experimental techniques are discussed. Development of a reflective telescope setup intended to increase the conversion efficiency of ultraviolet (UV) laser pulse generation is described, and the setup is used in the studies of CO[superscript]+ dissociation described in this report. The other technical study presented here is the measurement of the position dependence of timing signals picked off of a microchannel plate (MCP) surface. The experimental method is presented and significant time spread over the surface of the MCP detector is reported [1].
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Chen, Hongxin. "Electromagnetically induced transparency in laser-cooled rubidium." Thesis, Open University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265348.

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Makhija, Varun. "Laser-induced rotational dynamics as a route to molecular frame measurements." Diss., Kansas State University, 2014. http://hdl.handle.net/2097/18522.

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Анотація:
Doctor of Philosophy
Department of Physics
Vinod Kumarappan
In general, molecules in the gas phase are free to rotate, and measurements made on such samples are averaged over a randomly oriented distribution of molecules. Any orientation dependent information is lost in such measurements. The goal of the work presented here is to a) mitigate or completely do away with orientational averaging, and b) make fully resolved orientation dependent measurements. In pursuance of similar goals, over the past 50 years chemists and physicists have developed techniques to align molecules, or to measure their orientation and tag other quantities of interest with the orientation. We focus on laser induced alignment of asymmetric top molecules. The first major contribution of our work is the development of an effective method to align all molecular axes under field-free conditions. The method employs a sequence of nonresonant, impulsive laser pulses with varied ellipticities. The efficacy of the method is first demonstrated by solution of the time dependent Schr\"{o}dinger equation for iodobenzene, and then experimentally implemented to three dimensionally align 3,5 difluoroiodobenzene. Measurement from molecules aligned in this manner greatly reduces orientational averaging. The technique was developed via a thorough understanding and extensive computations of the dynamics of rotationally excited asymmetric top molecules. The second, and perhaps more important, contribution of our work is the development of a new measurement technique to extract the complete orientation dependence of a variety of molecular processes initiated by ultrashort laser pulses. The technique involves pump-probe measurements of the process of interest from a rotational wavepacket generated by impulsive excitation of asymmetric top molecules. We apply it to make the first measurement of the single ionization probability of an asymmetric top molecule in a strong field as a function of all relevant alignment angles. The measurement and associated calculations help identify the orbital from which the electron is ionized. We expect that this technique will be widely applicable to ultrafast-laser driven processes in molecules and provide unique insight into molecular physics and chemistry.
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Книги з теми "Laser Induced Molecular Dissociation"

1

Williamson, James Michael Bruce. Laser induced fluorescence characterization of molecular photofragments. 1987.

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2

Balakrishnan, Ashtok *. Extreme ultraviolet laser spectroscopy: a determination of the dissociation energy of molecular hydrogen. 1988.

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3

Northrup, Frederick James. Applications of vacuum ultraviolet laser-induced fluorescence to studies of molecular dynamics. 1985.

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4

He, Guang S. Laser Stimulated Scattering and Multiphoton Excitation. Oxford University Press, 2022. http://dx.doi.org/10.1093/oso/9780192895615.001.0001.

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Laser Stimulated Scattering and Multiphoton Excitation is the first book that comprehensively covers the following three major areas: (1) Quantum electrodynamic theory of stimulated scattering and multiphoton excitation processes; (2) Various stimulated scattering effects, including the early discovered stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), the later investigated stimulated Kerr scattering (SKS), and the recently developed stimulated Rayleigh–Bragg scattering (SRBS) and stimulated Mie scattering (SMS); (3) Multiphoton excitation-based nonlinear optical effects, photoelectric effects, atomic and molecular ionization effects, and molecular dissociation effects. Each chapter covers: (i) the concept and mechanism description, (ii) the necessary theoretical formulation, (iii) the experimental research achievements, and (iv) the scientific/technological applications. Laser Stimulated Scattering and Multiphoton Excitation is useful and suitable for academics, experts, and students working or interested in the areas of nonlinear optics, nonlinear photonics, laser spectroscopy, physical optics, physical chemistry, and optoelectronic engineering.
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Частини книг з теми "Laser Induced Molecular Dissociation"

1

Sudbø, A. S., P. A. Schulz, Y. R. Shen, and Y. T. Lee. "Molecular-Beam Studies of Laser-Induced Multiphoton Dissociation." In Topics in Current Physics, 95–122. Berlin, Heidelberg: Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/978-3-642-82292-6_3.

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2

Bjerre, N., and S. R. Keiding. "Laser/Electric Field Dissociation Spectroscopy of Molecular Ions." In Laser Spectroscopy VIII, 202–5. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-540-47973-4_54.

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3

Kulander, K. C., F. H. Mies, and K. J. Schafer. "Dynamics of Multiphoton Molecular Ionization and Dissociation." In Super-Intense Laser-Atom Physics IV, 163–69. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0261-9_16.

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4

Zhao, Min, Wankun Xie, Travis W. Hein, Lih Kuo, and Robert H. Rosa. "Laser-Induced Choroidal Neovascularization in Rats." In Methods in Molecular Biology, 77–85. New York, NY: Springer US, 2021. http://dx.doi.org/10.1007/978-1-0716-1480-8_9.

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5

Guo, Chunlei. "Slowing down molecular dissociation in strong laser fields." In Ultrafast Phenomena XV, 564–66. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-68781-8_182.

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6

Papagiannakopoulos, P., and D. Zevgolis. "Laser Emission at 502nm Induced by KrF Laser Multiphoton Dissociation of HgBr2." In Advances in Chemical Reaction Dynamics, 475–82. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4734-4_30.

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7

Stenholm, S. "Laser-Induced Processes in Molecular Systems." In Springer Proceedings in Physics, 313–20. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-79101-7_33.

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8

Hoheisel, W., U. Schulte, M. Vollmer, and F. Träger. "Optical spectra and laser-induced dissociation of supported Na particles." In Small Particles and Inorganic Clusters, 831–33. Berlin, Heidelberg: Springer Berlin Heidelberg, 1991. http://dx.doi.org/10.1007/978-3-642-76178-2_199.

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Kurizki, G., and A. Ben-Reuven. "Time-Resolved Photofragment Fluorescence as a Probe of Laser-Pulse Molecular Dissociation." In Methods of Laser Spectroscopy, 443–48. Boston, MA: Springer US, 1986. http://dx.doi.org/10.1007/978-1-4615-9459-8_60.

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10

Mort, Andrew, and Xiangmei Wu. "Capillary Electrophoresis with Detection by Laser-Induced Fluorescence." In Methods in Molecular Biology, 93–102. Totowa, NJ: Humana Press, 2010. http://dx.doi.org/10.1007/978-1-61779-008-9_6.

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Тези доповідей конференцій з теми "Laser Induced Molecular Dissociation"

1

Morin, P. "Free Electron Laser Induced Dissociation of Molecules Probed with Synchrotron Radiation." In Free-Electron Laser Applications in the Ultraviolet. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/fel.1988.wc2.

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Photodissociation of isolated polyatomic molecules is of great interest not only for itself but also because it is closely related to various important areas such as photochemistry (1), combustion phenomena (2), atmospheric pollution (3), interstellar chemistry (4) and isotope separation (5). Considerable progresses was made in the 70's by the extensive use of lasers for a very selective excitation of the molecule. State to state correlations between the various steps of dissociation dynamics have been achieved by a combination of various techniques to probe the dissociation products., such as laser induced fluorescence (6), VUV ionization (4), resonant multiphoton ionization (7), coherent anti-stokes Raman spectroscopy (8), V_V transfert (9), IR or visible fluorescence (10) or mass spectrometry (11) associated with molecular beam technique. At this time, available lasers are not tunable over a wide range in the UV, thus limiting the species of molecules that can be studied.
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2

Kazaryan, Mishik A., Yuri A. Dyakov, Maksim G. Golubkov, Dina P. Gubanova, Nikolay A. Bulychev, and Serine M. Kazaryan. "Laser-induced dissociation processes of protonated glucose: dehydration reactions vs cross-ring dissociation." In XIII International Conference on Atomic and Molecular Pulsed Lasers, edited by Andrei M. Kabanov and Victor F. Tarasenko. SPIE, 2018. http://dx.doi.org/10.1117/12.2303528.

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3

Ludwig, J., H. Rottke, and W. Sandner. "Molecular Hydrogen in an Intense Light Field." In Applications of High Field and Short Wavelength Sources. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/hfsw.1997.fd6.

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The dissociation and ionization mechanisms of molecules and molecular ions in a high intensity non-perturbative optical radiation field has attracted much interest experimentally as well as theoretically ([1,2] and refs, cited there). Especially investigations on molecular hydrogen have revealed many new molecule specific high field phenomena originating in the coupled electronic and nuclear degrees of freedom. Zaviyev et al. and Yang et al. found mechanisms like bond-softening dissociation, above threshold dissociation, or multiphoton dissociation to be active in the hydrogen molecular ion [3,4,5]. Also an indication of light-induced vibrational structure in H2+ and D2+ was detected [6]. At the high intensities reached in a focused laser beam finally the molecular ion may become ionized resulting in Coulomb explosion of the remaining bare nuclei. Hints pointing to this mechanism to be active have been found in H+ and D+ kinetic energy distributions [2,6].
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4

Liu, W. K., W. H. Fletcher, and D. W. Noid. "Laser-induced dissociation dynamics in triatomic molecules." In AIP Conference Proceedings Volume 146. AIP, 1986. http://dx.doi.org/10.1063/1.35736.

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5

Brannon, James H. "Chemical Etching of Silicon by CO2 Laser Induced Dissociation of NF3." In Microphysics of Surfaces, Beams, and Adsorbates. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/msba.1987.mb3.

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Surface studies have established that radicals frequently react with surfaces which are inert to the parent molecule. Dissociation of the parent molecule provides a reaction channel which avoids the often large activation barrier inherent in parent molecule-surface interactions. The interaction of gaseous NF3 with amorphous silicon is an excellent example of this type of behavior. While NF3 does not measurably chemically react with silicon at ambient temperatures, the fluorine containing radicals produced from laser dissociated NF3 readily do so. Some fraction of the fluorosilyl reaction products spontaneously desorb, resulting in silicon removal (etching). In this study parallel incident dissociating radiation did not contact the silicon surface, indicating that the observed etching reactions result from purely chemical effects. Effects due to transient surface heating or physical ablation can be discounted.
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6

Kodama, Yutaka, and Heihachi Sato. "Effect of Molecular Sieve on Transient Output-Reduction and Laser Parameters in DC Discharged /Room Temperature Operated FAF CO Laser." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1998. http://dx.doi.org/10.1364/cleo_europe.1998.cthj5.

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The output power tends to transiently decrease with discharge time in a dc electrically pumped fast axial-flow (FAF) CO laser. This output reduction is mainly caused by both the temperature rise of gas mixture and deactivation of the excited CO molecule due to its dissociation into CO2 and O2 molecules.1 Especially, the latter seems to be predominant in the room temperature operated FAF CO laser system. The gas temperature rise due to the discharge can be compensated by fast gas-circulation through a heat exchanger along with either ethanol/dry ice coolants (or liquid nitrogen at subroom temperature operation) , whereas the CO2 molecules generated through the discharge process cannot be avoided at room temperature operation, though, it is well trapped with a cold trap of liquid nitrogen. Thus, we shall try to recover the output reduction transiently induced above by adsorbing the generated CO2 molecules by molecular sieve for the room temperature operation together with theoretical explanation. In addition, we shall also examine how the laser parameters such as the small-signal gain γ0.v saturation intensity Is and a measure of partial homogeneity m are influenced with insertion of molecular sieve.
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7

Liang, Zhi, Hai-Lung Tsai, and Lan Jiang. "Determination of Laser Absorption Coefficients of Gas Mixtures Using an Ab Initio MD Model." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41449.

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In an effort to study the laser induced dissociation of gas mixtures for an ongoing research project on diamond thin film coating using multiple lasers, it is necessary to determine the absorption coefficient of laser energy by CO2 gas. An ab initio molecular dynamics (AIMD) model is used to determine the laser absorption coefficient of CO2 gas as a function of laser wavelength and gas temperature. The translational, rotational, and vibration motions of molecules are all taken into account in our model. The intra-molecular potential energy is obtained by solving the Kohn-Sham equation. The Projector-Augmented Wave (PAW) exchange-correlation potential function is used in the ab initio calculation. Specific heat of the CO2 gas is also calculated. The calculated thermal properties of CO2 gas and the vibration spectrum of molecules are in good agreement with the experimental results. The calculated normalized absorption line shape CO2 gas is close to the experimental results.
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8

Botter, R., I. Dimicoli, and J. Lemaire. "Rempi Studies Of Laser Induced Dissociation Oe Polyatomic Molecules And Ions." In 1986 Quebec Symposium, edited by D. K. Evans. SPIE, 1986. http://dx.doi.org/10.1117/12.938936.

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9

Sanche., Léon. "Interaction of Low-Energy Electrons With Adsorbed Molecules: Mechanisms of Energy Transfer and Dissociation." In The Microphysics of Surfaces: Beam-Induced Processes. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/msbip.1991.mc2.

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The chemical reactivity of molecules physisorbed or chemisorbed on solid surfaces is a topic of interest in many areas of applied physics and chemistry. A large portion of the activity in this field of research has been focused on the catalytic action of surfaces; however, the recent discoveries on the possibility to enhance, trigger and even control chemical reactions with photon and particle beams incident on surfaces are now starting to shift scientific interests toward studies of the dynamics involved in these non-thermal reactions. Particularly, photon and electron beam methods are expected to surpass present macroscopic methods (e.g., plasma etching) in the manufacture of microelectronic and micromechanical devices requiring fine-line lithography [1]. One class of such techniques involves the utilization of laser photons with energies ranging from 0.1 eV in the infrared to 6 eV in the ultraviolet [2]. Many of the laser-driven surface reactions are expected to be caused by the photogeneration of low-energy electrons which transfer energy to an adsorbate causing dissociation and desorption [3-7].
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10

Walkup, Robert E. "Femtosecond time-resolved absorption spectroscopy." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.thdd1.

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Femtosecond time-resolved absorption spectroscopy is discussed in terms of a simple model in which the collision complex is regarded as a time- dependent dipole oscillator. This model is applied to recent measurements of the absorption spectra molecules in the process of dissociating. When the dissociation process yields a narrow wave packet, the dominant feature in the absorption spectra is generally a sharp feature at the transition frequency for separated atoms. The spectrum in this impact region reflects an effective phase- shift for a partial collision which begins at the time of excitation by the probe pulse. By inspection of the data, one can directly see when the atoms have reached the Weisskopf radius, the point where the partial collision provides a phase- shift of 1 radian. Moreover, by measuring the phase-shift as a function of pump-probe delay, one can recover the molecular transition frequency along the path of dissociation. For broad wave packets, there can be a large phase-shift spread, and the spectra approach a statistical limit, in which the absorption profile directly reflects the distribution of molecular transition frequencies at the time of excitation by the probe pulse. Measurements of the spectral power density of the transmitted probe pulse, are compared and contrasted with measurements based on laser-induced fluorescence.
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Звіти організацій з теми "Laser Induced Molecular Dissociation"

1

Lewis, Aaron. Fundamental Studies in the Molecular Basis of Laser Induced Retinal Damage. Fort Belvoir, VA: Defense Technical Information Center, January 1988. http://dx.doi.org/10.21236/ada203634.

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2

Lewis, Aaron. Fundamental Studies in the Molecular Basis of Laser Induced Retinal Damage. Fort Belvoir, VA: Defense Technical Information Center, April 1991. http://dx.doi.org/10.21236/ada239941.

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3

Shomer, Ilan, Ruth E. Stark, Victor Gaba, and James D. Batteas. Understanding the hardening syndrome of potato (Solanum tuberosum L.) tuber tissue to eliminate textural defects in fresh and fresh-peeled/cut products. United States Department of Agriculture, November 2002. http://dx.doi.org/10.32747/2002.7587238.bard.

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The project sought to understand factors and mechanisms involved in the hardening of potato tubers. This syndrome inhibits heat softening due to intercellular adhesion (ICA) strengthening, compromising the marketing of industrially processed potatoes, particularly fresh peeled-cut or frozen tubers. However, ICA strengthening occurs under conditions which are inconsistent with the current ideas that relate it to Ca-pectate following pectin methyl esterase (PME) activity or to formation of rhamnogalacturonan (RG)-II-borate. First, it was necessary to induce strengthening of the middle lamellar complex (MLX) and the ICA as a stress response in some plant parenchyma. As normally this syndrome does not occur uniformly enough to study it, we devised an efficient model in which ICA-strengthening is induced consistently under simulated stress by short-chain, linear, mono-carboxylic acid molecules (OAM), at 65 oC [appendix 1 (Shomer&Kaaber, 2006)]. This rapid strengthening was insufficient for allowing the involved agents assembly to be identifiable; but it enabled us to develop an efficient in vitro system on potato tuber parenchyma slices at 25 ºC for 7 days, whereas unified stress was reliably simulated by OAMs in all the tissue cells. Such consistent ICA-strengthening in vitro was found to be induced according to the unique physicochemical features of each OAM as related to its lipophilicity (Ko/w), pKa, protonated proportion, and carbon chain length by the following parameters: OAM dissociation constant (Kdiss), adsorption affinity constant (KA), number of adsorbed OAMs required for ICA response (cooperativity factor) and the water-induced ICA (ICAwater). Notably, ICA-strengthening is accompanied by cell sap leakage, reflecting cell membrane rupture. In vitro, stress simulation by OAMs at pH<pKa facilitated the consistent assembly of ICAstrengthening agents, which we were able to characterize for the first time at the molecular level within purified insoluble cell wall of ICA-strengthened tissue. (a) With solid-state NMR, we established the chemical structure and covalent binding to cell walls of suberin-like agents associated exclusively with ICA strengthening [appendix 3 (Yu et al., 2006)]; (b) Using proteomics, 8 isoforms of cell wall-bound patatin (a soluble vacuolar 42-kDa protein) were identified exclusively in ICA-strengthened tissue; (c) With light/electron microscopy, ultrastructural characterization, histochemistry and immunolabeling, we co-localized patatin and pectin in the primary cell wall and prominently in the MLX; (d) determination of cell wall composition (pectin, neutral sugars, Ca-pectate) yielded similar results in both controls and ICA-strengthened tissue, implicating factors other than PME activity, Ca2+ or borate ions; (e) X-ray powder diffraction experiments revealed that the cellulose crystallinity in the cell wall is masked by pectin and neutral sugars (mainly galactan), whereas heat or enzymatic pectin degradation exposed the crystalline cellulose structure. Thus, we found that exclusively in ICA-strengthened tissue, heat-resistant pectin is evident in the presence of patatin and suberinlike agents, where the cellulose crystallinity was more hidden than in fresh control tissue. Conclusions: Stress response ICA-strengthening is simulated consistently by OAMs at pH< pKa, although PME and formation of Ca-pectate and RG-II-borate are inhibited. By contrast, at pH>pKa and particularly at pH 7, ICA-strengthening is mostly inhibited, although PME activity and formation of Ca-pectate or RG-II-borate are known to be facilitated. We found that upon stress, vacuolar patatin is released with cell sap leakage, allowing the patatin to associate with the pectin in both the primary cell wall and the MLX. The stress response also includes formation of covalently bound suberin-like polyesters within the insoluble cell wall. The experiments validated the hypotheses, thus led to a novel picture of the structural and molecular alterations responsible for the textural behavior of potato tuber. These findings represent a breakthrough towards understanding of the hardening syndrome, laying the groundwork for potato-handling strategies that assure textural quality of industrially processed particularly in fresh peeled cut tubers, ready-to-prepare and frozen preserved products.
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4

Droby, Samir, Michael Wisniewski, Ron Porat, and Dumitru Macarisin. Role of Reactive Oxygen Species (ROS) in Tritrophic Interactions in Postharvest Biocontrol Systems. United States Department of Agriculture, December 2012. http://dx.doi.org/10.32747/2012.7594390.bard.

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To elucidate the role of ROS in the tri-trophic interactions in postharvest biocontrol systems a detailed molecular and biochemical investigation was undertaken. The application of the yeast biocontrol agent Metschnikowia fructicola, microarray analysis was performed on grapefruit surface wounds using an Affymetrix Citrus GeneChip. the data indicated that 1007 putative unigenes showed significant expression changes following wounding and yeast application relative to wounded controls. The expression of the genes encoding Respiratory burst oxidase (Rbo), mitogen-activated protein kinase (MAPK) and mitogen-activated protein kinase kinase (MAPKK), G-proteins, chitinase (CHI), phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and 4-coumarate-CoA ligase (4CL). In contrast, three genes, peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), were down-regulated in grapefruit peel tissue treated with yeast cells. The yeast antagonists, Metschnikowia fructicola (strain 277) and Candida oleophila (strain 182) generate relatively high levels of super oxide anion (O2−) following its interaction with wounded fruit surface. Using laser scanning confocal microscopy we observed that the application of M. fructicola and C. oleophila into citrus and apple fruit wounds correlated with an increase in H2O2 accumulation in host tissue. The present data, together with our earlier discovery of the importance of H₂O₂ production in the defense response of citrus flavedo to postharvest pathogens, indicate that the yeast-induced oxidative response in fruit exocarp may be associated with the ability of specific yeast species to serve as biocontrol agents for the management of postharvest diseases. Effect of ROS on yeast cells was also studied. Pretreatment of the yeast, Candida oleophila, with 5 mM H₂O₂ for 30 min (sublethal) increased yeast tolerance to subsequent lethal levels of oxidative stress (50 mM H₂O₂), high temperature (40 °C), and low pH (pH 4). Suppression subtractive hybridization analysis was used to identify genes expressed in yeast in response to sublethal oxidative stress. Transcript levels were confirmed using semi quantitative reverse transcription-PCR. Seven antioxidant genes were up regulated. Pretreatment of the yeast antagonist Candida oleophila with glycine betaine (GB) increases oxidative stress tolerance in the microenvironment of apple wounds. ROS production is greater when yeast antagonists used as biocontrol agents are applied in the wounds. Compared to untreated control yeast cells, GB-treated cells recovered from the oxidative stress environment of apple wounds exhibited less accumulation of ROS and lower levels of oxidative damage to cellular proteins and lipids. Additionally, GB-treated yeast exhibited greater biocontrol activity against Penicillium expansum and Botrytis cinerea, and faster growth in wounds of apple fruits compared to untreated yeast. The expression of major antioxidant genes, including peroxisomal catalase, peroxiredoxin TSA1, and glutathione peroxidase was elevated in the yeast by GB treatment. A mild heat shock (HS) pretreatment (30 min at 40 1C) improved the tolerance of M. fructicola to subsequent high temperature (45 1C, 20–30 min) and oxidative stress (0.4 mol-¹) hydrogen peroxide, 20–60 min). HS-treated yeast cells showed less accumulation of reactive oxygen species (ROS) than non-treated cells in response to both stresses. Additionally, HS-treated yeast exhibited significantly greater (P≥0.0001) biocontrol activity against Penicillium expansum and a significantly faster (Po0.0001) growth rate in wounds of apple fruits stored at 25 1C compared with the performance of untreated yeast cells. Transcription of a trehalose-6-phosphate synthase gene (TPS1) was up regulated in response to HS and trehalose content also increased.
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