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Journal articles on the topic 'CH Stretch Infrared Spectrum'

Author: Grafiati

Published: 6 September 2023

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1

Loh, Zoë M., Rosemary L. Wilson, Duncan A. Wild, Evan J. Bieske, and Mark S. Gordon. "Structures of F - -(CH4)n and Cl - -(CH4)n (n = 1,2) Anion Clusters Elucidated through Ab Initio Calculations and Infrared Spectra." Australian Journal of Chemistry 57, no. 12 (2004): 1157. http://dx.doi.org/10.1071/ch04149.

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Ab initio calculations are performed at the MP2/aug-cc-pVTZ level for F−-CH4 and Cl−-CH4, to show that the dimers have C3v symmetry with the CH4 sub-unit attached to the halide anion by a single hydrogen bond. This geometry is consistent with infrared spectra of F−-CH4 and Cl−-CH4 recorded in the CH-stretch region. The calculations also indicate substantial anharmonicity in the H-bonded CH stretch of F−-CH4. Infrared spectra of the F−-(CH4)2 and Cl−-(CH4)2 trimer clusters are consistent with structures that have two equivalent CH4 sub-units H-bonded to the halide core. Additional bands in the F−-(CH4)2 spectrum are assigned as transitions to CH4 bending overtone and combination levels, gaining infrared intensity from Fermi interaction with the H-bonded CH stretch.

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2

Hsu, Kuo-Hsiang, Yu-Hsuan Huang, Yuan-Pern Lee, Meng Huang, Terry A. Miller, and Anne B. McCoy. "Manifestations of Torsion-CH Stretch Coupling in the Infrared Spectrum of CH3OO." Journal of Physical Chemistry A 120, no. 27 (March 16, 2016): 4827–37. http://dx.doi.org/10.1021/acs.jpca.5b12334.

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3

Jagod, Mary-Frances, Charles M. Gabrys, Matthias Rösslein, Dairene Uy, and Takeshi Oka. "Infrared spectrum of CH3+ involving high rovibrationai levels." Canadian Journal of Physics 72, no. 11-12 (November 1, 1994): 1192–99. http://dx.doi.org/10.1139/p94-153.

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An extensive search of carbo-ion spectra in the infrared region from 3300 cm−1 to 2900 cm−1 has revealed many spectral lines of CH3+, the most fundamental hydrocarbon cation. Out of over 1000 spectral lines that were identified as due to CH3+from their plasma chemical behaviors and linewidths, 356 lines have been assigned to the CH stretch ν3 fundamental band. Most of the remaining lines are thought to belong to the hot bands ν2 + ν3 − ν2 and ν3 + ν4 − ν4. Their analysis was found to be difficult because of the large Coriolis interaction and the near degeneracy of ν2 and ν4. A series of spectral lines has been assigned to the ν3 + ν4 − ν4 band. The rovibrational temperature of CH3+ in the plasma has been determined from relative intensities of the spectral lines.

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4

Chen, Zaijun, Theodor W. Hänsch, and Nathalie Picqué. "Mid-infrared feed-forward dual-comb spectroscopy." Proceedings of the National Academy of Sciences 116, no. 9 (February 12, 2019): 3454–59. http://dx.doi.org/10.1073/pnas.1819082116.

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Mid-infrared high-resolution spectroscopy has proven an invaluable tool for the study of the structure and dynamics of molecules in the gas phase. The advent of frequency combs advances the frontiers of precise molecular spectroscopy. Here we demonstrate, in the important 3-µm spectral region of the fundamental CH stretch in molecules, dual-comb spectroscopy with experimental coherence times between the combs that exceed half an hour. Mid-infrared Fourier transform spectroscopy using two frequency combs with self-calibration of the frequency scale, negligible contribution of the instrumental line shape to the spectral profiles, high signal-to-noise ratio, and broad spectral bandwidth opens up opportunities for precision spectroscopy of small molecules. Highly multiplexed metrology of line shapes may be envisioned.

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5

BLAKE, THOMAS A., PAUL L. GASSMAN, and NEAL B. GALLAGHER. "DETECTION AND CLASSIFICATION OF ORGANIC AND ORGANOPHOSPHORUS ANALYTES ON SOIL FROM REFLECTION-ABSORPTION SPECTROSCOPY." International Journal of High Speed Electronics and Systems 18, no. 02 (June 2008): 319–36. http://dx.doi.org/10.1142/s0129156408005370.

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Principal Components Analysis (PCA) is a common anomaly detection tool that was used in this work to detect organic and organophosphate analytes on soils using mid-infrared reflection-absorption spectroscopy. Detection is hindered by large variability in sample-to-sample soil reflectivity that is due to the random nature of the soil particle packing. Extended multiplicative scatter correction (EMSC) and Savitzky-Golay derivative preprocessing were examined as methods to reduce this variability and enhance detection capability. Second derivative preprocessing provided results that were at least as good as EMSC for detection and the simplicity of the derivative methodology makes it an attractive preprocessing approach. Typically, PCA is applied to all spectral channels and results from detection events are interrogated to identify a potential cause. In this work, PCA models were developed for specific wavenumber ranges corresponding to functional group frequencies with the objective of providing some classification capability. It was found that detection of CH 2, CH 3 and P = O stretching bands was possible; however, results for a – CH 2 scissors band was less encouraging and detection of O – H stretch, – C – C – skeletal stretch, and PO – C stretch modes was poor. Some limited classification capability may be possible, but it would be difficult to make a unique assignment of the analytes present using the strategies studied.

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6

Parker, Stewart F., Emilie J. Revill-Hivet, Daniel W. Nye, and Matthias J. Gutmann. "Structure and vibrational spectroscopy of lithium and potassium methanesulfonates." Royal Society Open Science 7, no. 7 (July 2020): 200776. http://dx.doi.org/10.1098/rsos.200776.

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In this work, we have determined the structures of lithium methanesulfonate, Li(CH 3 SO 3 ), and potassium methanesulfonate, K(CH 3 SO 3 ), and analysed their vibrational spectra. The lithium salt crystallizes in the monoclinic space group C 2/ m with two formula units in the primitive cell. The potassium salt is more complex, crystallizing in I 4/ m with 12 formula units in the primitive cell. The lithium ion is fourfold coordinated in a distorted tetrahedron, while the potassium salt exhibits three types of coordination: six-, seven- and ninefold. Vibrational spectroscopy of the compounds (including the 6 Li and 7 Li isotopomers) confirms that the correlation previously found, that in the infrared spectra there is a clear distinction between coordinated and not coordinated forms of the methanesulfonate ion, is also valid here. The lithium salt shows a clear splitting of the asymmetric S–O stretch mode, indicating a bonding interaction, while there is no splitting in the spectrum of the potassium salt, consistent with a purely ionic material.

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7

Bahri, Syaiful, Yuli Ambarwati, Lina Marlina, Vera Fitriani, and Sutopo Hadi. "The Attractant Bioactivity Test of Semi-Polar Fraction of the Datuan Stem Bark (Ficus vasculosa Wall. Ex Miq) against Warehouse Pest (Sitophilus oryzae L.)." Journal of Pure and Applied Microbiology 15, no. 4 (October 4, 2021): 2125–35. http://dx.doi.org/10.22207/jpam.15.4.35.

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Bioactive isolation was performed on the stem bark of Datuan (Ficus vasculosa Wall. Ex Miq), and extraction was carried out via the maceration method using acetone as a solvent. Furthermore, an attractant bioactivity test was conducted on acetone extract, A-G fraction, and composition of the isolates. The separation and purification via column chromatography produced a D8.3.5.7 fraction in the form of needle crystal of about 50 mg, at a melting point of 136°C–138.7°C. Thin-layer chromatography (TLC) analysis showed a single spot at an Rf value of 0.57 (n-hexane eluent: ethyl acetate 7:3), 0.36 (DCM eluent), and 0.24 (CHCl3 eluent). The isolated compounds were identified using infrared and UV–Vis spectrophotometry, as well as mass spectrometry. The characterization of the infrared spectrum of the isolated compound showed a strong OH goo band at 3461 cm-1 region and the absorption band at 2936.25 cm-1 exhibited a stretch of CH alkanes. These two bands are supported by the vibration at 1378.47 and 1462.55 cm-1 for CH absorption of methyl and methylene. The absorption band in the 1622 cm-1 region showed a stretch of conjugated C=C double bond, which is supported by absorption at 918.96 and 966.22 cm-1 as C–H alkene. The UV–Vis spectrophotometry showed absorption at λmax 263.97 nm A = 0.483, which was the result of electronic transition π → π*, and at λ 331.0 nm A = 0.274, which was an electronic result of n → π*. Meanwhile, identification via mass spectrometry that produces isolate has a molecular weight of 414.1 m/e with the formula C29H50O. Therefore, the bioactivity test results on compound D8.3.5.7 had an attractant activity of 71.67% against warehouse pests (Sitophilus oryzae L.) and an interest index of 0.63.

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8

Mustarichie, Resmi, and Dudi Runadi. "Isolation and identification of flavonoids from avocado leaves (Persea americana Mill)." Asian Journal of Pharmaceutical Research and Development 9, no. 6 (December 14, 2021): 34–40. http://dx.doi.org/10.22270/ajprd.v9i6.1035.

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Leaves of avocado (Persea americana Mill) contains bioactive compounds that can act as natural antioxidants. This study was conducted to isolate and identify the flavonoid compounds of avocado leaves. Research stages includes maceration, fractionation, thin-layer chromatography analysis, isolation and purification of compounds also identification of isolates in two-dimensional thin-layer chromatography and by using three different types of solvents. Isolates were identified using ultraviolet-visible spectrophotometry and infrared spectrophotometry. From the results obtained one isolate FA6 showed a single compound. Based on the results by testing the purity of isolates using two-dimensional thin-layer chromatography and by using three different types of solvents, isolates FA6 is a pure compound. Identification by using ray-visible spectrophotometry FA6 isolates showed maximum wavelength at 280.6 nm and 342.0 nm on bands II and on band I. Infrared spectrum ofisolate FA6 showed aromatic OH groups, aliphatic CH, C = O stretching, C = C aromatic, and C-O-C stretch. From the results obtained isolates FA6 is a class of flavonoids group flavones or flavonol (3-OH substitional).

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9

Korn, Joseph A., Daniel P. Tabor, Edwin L. Sibert, and Timothy S. Zwier. "Conformation-specific spectroscopy of alkyl benzyl radicals: Effects of a radical center on the CH stretch infrared spectrum of an alkyl chain." Journal of Chemical Physics 145, no. 12 (September 28, 2016): 124314. http://dx.doi.org/10.1063/1.4963227.

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10

Cheng, Tao, Alessandro Fortunelli, and William A. Goddard. "Reaction intermediates during operando electrocatalysis identified from full solvent quantum mechanics molecular dynamics." Proceedings of the National Academy of Sciences 116, no. 16 (March 13, 2019): 7718–22. http://dx.doi.org/10.1073/pnas.1821709116.

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Electrocatalysis provides a powerful means to selectively transform molecules, but a serious impediment in making rapid progress is the lack of a molecular-based understanding of the reactive mechanisms or intermediates at the electrode–electrolyte interface (EEI). Recent experimental techniques have been developed for operando identification of reaction intermediates using surface infrared (IR) and Raman spectroscopy. However, large noises in the experimental spectrum pose great challenges in resolving the atomistic structures of reactive intermediates. To provide an interpretation of these experimental studies and target for additional studies, we report the results from quantum mechanics molecular dynamics (QM-MD) with explicit consideration of solvent, electrode–electrolyte interface, and applied potential at 298 K, which conceptually resemble the operando experimental condition, leading to a prototype of operando QM-MD (o-QM-MD). With o-QM-MD, we characterize 22 possible reactive intermediates in carbon dioxide reduction reactions (CO2RRs). Furthermore, we report the vibrational density of states (v-DoSs) of these intermediates from two-phase thermodynamic (2PT) analysis. Accordingly, we identify important intermediates such as chemisorbed CO2 (b-CO2), *HOC-COH, *C-CH, and *C-COH in our o-QM-MD likely to explain the experimental spectrum. Indeed, we assign the experimental peak at 1,191 cm−1 to the mode of C-O stretch in *HOC-COH predicted at 1,189 cm−1 and the experimental peak at 1,584 cm−1 to the mode of C-C stretch in *C-COD predicted at 1,581 cm−1. Interestingly, we find that surface ketene (*C=C=O), arising from *HOC-COH dehydration, also shows signals at around 1,584 cm−1, which indicates a nonelectrochemical pathway of hydrocarbon formation at low overpotential and high pH conditions.

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11

Adilina, Indri Badria, Robert Ronal Widjaya, Luthfiana Nurul Hidayati, Edi Supriadi, Muhammad Safaat, Ferensa Oemry, Elvi Restiawaty, Yazid Bindar, and Stewart F. Parker. "Understanding the Surface Characteristics of Biochar and Its Catalytic Activity for the Hydrodeoxygenation of Guaiacol." Catalysts 11, no. 12 (November 25, 2021): 1434. http://dx.doi.org/10.3390/catal11121434.

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Biochar (BCR) was obtained from the pyrolysis of a palm-oil-empty fruit bunch at 773 K for 2 h and used as a catalyst for the hydrodeoxygenation (HDO) of guaiacol (GUA) as a bio-oil model compound. Brunauer–Emmet–Teller surface area analysis, NH3 and CO2-temperature-programmed desorption, scanning electron microscope–dispersive X-ray spectroscopy, CHN analysis and X-ray fluorescence spectroscopy suggested that macroporous and mesoporous structures were formed in BCR with a co-presence of hydrophilic and hydrophobic sites and acid–base behavior. A combination of infrared, Raman and inelastic neutron scattering (INS) was carried out to achieve a complete vibrational assignment of BCR. The CH–OH ratio in BCR is ~5, showing that the hydroxyl functional groups are a minority species. There was no evidence for any aromatic C–H stretch modes in the infrared, but they are clearly seen in the INS and are the majority species, with a ratio of sp3–CH:sp2–CH of 1:1.3. The hydrogen bound to sp2–C is largely present as isolated C–H bonds, rather than adjacent C–H bonds. The Raman spectrum shows the characteristic G band (ideal graphitic lattice) and three D bands (disordered graphitic lattice, amorphous carbon, and defective graphitic lattice) of sp2 carbons. Adsorbed water in BCR is present as disordered layers on the surface rather than trapped in voids in the material and could be removed easily by drying prior to catalysis. Catalytic testing demonstrated that BCR was able to catalyze the HDO of GUA, yielding phenol and cresols as the major products. Phenol was produced both from the direct demethoxylation of GUA, as well as through the demethylation pathway via the formation of catechol as the intermediate followed by deoxygenation.

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12

Bauke, Stephan, Kai Golibrzuch, Frank Rotter, Hainer Wackerbarth, Olaf Thiele, and Thomas Berg. "Quantitative, time-resolved detection of CH<sub>4</sub> concentrations in flows for injection analysis in CNG engines using IR absorption." Journal of Sensors and Sensor Systems 6, no. 1 (May 8, 2017): 185–98. http://dx.doi.org/10.5194/jsss-6-185-2017.

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Abstract. The reduction of CO2 and other greenhouse gas emissions is an important driving force for the development of modern engines. Especially in the transport sector, the use of alternative fuels like methane, the main component of compressed natural gas (CNG), is an applied measure to achieve this goal. This work describes the development of an optical measurement system for accurate quantification of CH4 densities in gas flows based on broadband absorption of infrared light, i.e. non-dispersive IR absorption spectroscopy (NDIR). We demonstrate the capability of the system to achieve high time resolution as well as high measurement accuracy and precision. The optical set-up of the system is designed for usage at the inlet manifold of CNG-fuelled spark ignition engines. It allows for detailed analysis of the mixture formation during single engine cycles. CH4 densities can be determined by monitoring the infrared light attenuation around 3.3 µm caused by the ν3 anti-symmetric C–H-stretch vibration. We calculate the nonlinear relation between transmittance and CH4 density from absorption cross sections calculated from the HITRAN database. The theoretical transmittance signals are corrected for spectral influences of the bandpass filter, the detector sensitivity, the fibre transmittance and the emission spectrum of the light source in order to calculate CH4 densities directly from the measured transmittance. A calibration function corrects remaining differences between experimental and simulated values and improves the accuracy. We show that the sensor system is capable for determination of air–fuel ratios (λ-values) and demonstrate the dynamic quantification of a CH4 injection into a flow channel under various flow conditions. Furthermore, we present the first measurements with a prototype probe capable of measurements inside the inlet manifold of a four-stroke spark ignition engine. We validate the detection strategy in experiments with premixed gases using a modified inlet geometry and demonstrate its application under standard engine operation with port fuel injection while varying the injection parameters.

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13

Bariseviciute, Ruta, Justinas Ceponkus, and Valdas Sablinskas. "Matrix isolation FTIR spectroscopical study of ethene secondary ozonide." Open Chemistry 5, no. 1 (March 1, 2007): 71–86. http://dx.doi.org/10.2478/s11532-006-0073-6.

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AbstractA new method is used for the separation of ethene secondary ozonide (SOZ) from the other products of ethene ozonization reaction. The reaction was performed in the neat films of the reactants at 77 K. Ethene SOZ was separated from other products of the reaction by vacuum distillation at 190–210 K and analyzed by means of the matrix isolation IR absorption spectroscopy. Spectroscopic data from photolysis of the matrix isolated ozonide was used as an argument for assignment of the infrared spectral bands either to ethene SOZ or to other products of the reaction. The spectra of ethene SOZ isolated in the Ar matrix were analyzed by combining experimental results with the theoretical calculations performed at the MP2 6-311+G (3df, 3pd) level. A new assignment of some experimental fundamental bands is proposed taking in to account the Fermi resonance between CH stretch and the five membered ring vibrations. For the first time more than 30 weak infrared absorption bands were observed and assigned to various combination vibrations and overtones. By using new spectral information concerning the overtones and the combination bands it is concluded that the dissociation of unstable ethene SOZ involving breaking of any of the four CO bonds of the five membered ring of ethene SOZ has low probability. Dissociation of the ring starts from breaking of the OO bond.

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14

Kortyna, A., A. J. Samin, T. A. Miller, and D. J. Nesbitt. "Correction: Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν3/ν4 CH stretch modes and CH2 internal rotor dynamics of benzyl radical." Physical Chemistry Chemical Physics 21, no. 24 (2019): 13374. http://dx.doi.org/10.1039/c9cp90148e.

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Correction for ‘Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν₃/ν₄ CH stretch modes and CH₂ internal rotor dynamics of benzyl radical’ by A. Kortyna et al., Phys. Chem. Chem. Phys., 2017, 19, 29812–29821.

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15

Carrington, Alan, and Timothy P. Softley. "Infrared predissociation spectrum of the CH+ ion." Chemical Physics 106, no. 3 (August 1986): 315–38. http://dx.doi.org/10.1016/0301-0104(86)87103-8.

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16

Doney, Kirstin D., Andrew Kortyna, and David J. Nesbitt. "High-resolution infrared spectroscopy of HCF in the CH stretch region." Journal of Chemical Physics 152, no. 1 (January 7, 2020): 014305. http://dx.doi.org/10.1063/1.5133397.

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17

Kortyna, A., A. J. Samin, T. A. Miller, and D. J. Nesbitt. "Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν3/ν4 CH stretch modes and CH2 internal rotor dynamics of benzyl radical." Physical Chemistry Chemical Physics 19, no. 44 (2017): 29812–21. http://dx.doi.org/10.1039/c7cp05776h.

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18

Rizkita, Aden Dhana, Sintia Ayu Dewi, Emas Agus Prastyo Wibowo, and Iham Maulana. "Isolasi dan Identifikasi Saponin dari Ekstrak Leunca (Solanium ningrum L) Secara Spektrofotometri Infra Merah." JURNAL ILMIAH SAINS 21, no. 2 (October 29, 2021): 166. http://dx.doi.org/10.35799/jis.v21i2.34635.

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Penelitian ini dilakukan untuk mengisolasi dan mengidentifikasi senyawa saponin dengan maserasi menggunakan etanol 95% sampai mendapat ekstrak kering sebanyak 20 gram dengan dipanaskan menggunakan evaporator. Ekstraksi kedua dilakukan menggunakan corong pisah dengan pelarut dietil eter dan n-butanol. Identifikasi saponin dilakukan dengan tiga parameter uji diantaranya uji busa, uji warna dan gugus fungsi menggunakan Spektrofotometer Infra Merah. Hasil pengukuran Spektrofotometri Infra Merah menunjukkan Ekstrak Daun Launca mengandung beberapa gugus fungsi sebagai berikut : gugus –OH (puncak yang lebar pada bilangan gelombang 3444,87 cm-1), regang –CH alifatik simetri (bilangan gelombang 2926,01 cm-1 dan2854,65 cm-1, regang C=C tidak terkonjugasi pada bilangan gelombang 1606,7 cm-1, adanya regang C-H (bilangan gelombang 1074,35 cm-1 dan 1045,42 cm-1), dan adanya vibrasi bengkokan simetris C-O pada bilangan gelombang 1386,82 cm-1.Kata kunci: Daun leunca; spektrofotometer infra merah; saponin Isolation and Identification of Saponin from Leunca (Solanium ningrum L) Extract by Infrared SpectrophotometryABSTRACTThis research was conducted to isolate and identify saponin compounds by maceration using 95% ethanol to obtain 20 grams of dry extract by heating using an evaporator. The second extraction was carried out using a separating funnel with diethyl ether and n-butanol as solvents. Saponin identification was carried out with three test parameters including foam test, color test and functional group using Infrared Spectrophotometer. Infrared Spectrophotometry measurement results show that the Launca Leaf Extract contains the following functional groups: -OH group (wide peak at wave number 3444.87 cm-1), aliphatic symmetrical -CH stretch (wave number 2926.01 cm-1 and 2854 ,65 cm-1, unconjugated C=C stretch at wave number 1606.7 cm-1, presence of CH stretch (wave number 1074.35 cm-1 and 1045.42 cm-1), and the presence of symmetrical bending vibration of CO at wave number 1386.82 cm-1.Keywords: Infrared spectrophotometer; leunca leaf; saponin

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19

Leicht, Daniel, Matin Kaufmann, Gerhard Schwaab, and Martina Havenith. "Infrared spectroscopy of the helium solvated cyclopentadienyl radical in the CH stretch region." Journal of Chemical Physics 145, no. 7 (August 21, 2016): 074304. http://dx.doi.org/10.1063/1.4960781.

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20

Morter, C. L., C. Domingo, S. K. Farhat, E. Cartwright, G. P. Glass, and R. F. Curl. "Rotationally resolved spectrum of the ν1 CH stretch of the propargyl radical (H2CCCH)." Chemical Physics Letters 195, no. 4 (July 1992): 316–21. http://dx.doi.org/10.1016/0009-2614(92)85609-e.

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21

Toumi, A., N. Piétri, and I. Couturier-Tamburelli. "Infrared study of matrix-isolated ethyl cyanide: simulation of the photochemistry in the atmosphere of Titan." Physical Chemistry Chemical Physics 17, no. 45 (2015): 30352–63. http://dx.doi.org/10.1039/c5cp03616j.

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22

Ahn, Wonmi, Johan F. Triana, Felipe Recabal, Felipe Herrera, and Blake S. Simpkins. "Modification of ground-state chemical reactivity via light–matter coherence in infrared cavities." Science 380, no. 6650 (June 16, 2023): 1165–68. http://dx.doi.org/10.1126/science.ade7147.

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Reaction-rate modifications for chemical processes due to strong coupling between reactant molecular vibrations and the cavity vacuum have been reported; however, no currently accepted mechanisms explain these observations. In this work, reaction-rate constants were extracted from evolving cavity transmission spectra, revealing resonant suppression of the intracavity reaction rate for alcoholysis of phenyl isocyanate with cyclohexanol. We observed up to an 80% suppression of the rate by tuning cavity modes to be resonant with the reactant isocyanate (NCO) stretch, the product carbonyl (CO) stretch, and cooperative reactant-solvent modes (CH). These results were interpreted using an open quantum system model that predicted resonant modifications of the vibrational distribution of reactants from canonical statistics as a result of light–matter quantum coherences, suggesting links to explore between chemistry and quantum science.

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23

Lemmens, A. K., A. M. Rijs, and W. J. Buma. "Infrared Spectroscopy of Jet-cooled “GrandPAHs” in the 3–100 μm Region." Astrophysical Journal 923, no. 2 (December 1, 2021): 238. http://dx.doi.org/10.3847/1538-4357/ac2f9d.

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Abstract Although large polycyclic aromatic hydrocarbons (PAHs) are likely to be responsible for IR emission of gaseous and dusty regions, their neutral experimental high-resolution gas-phase IR spectra—needed to construct accurate astronomical models—have so far remained out of reach because of their nonvolatility. Applying laser desorption to overcome this problem, we report here the first IR spectra of the jet-cooled large PAHs coronene (C24H12), peropyrene (C26H14), ovalene (C32H14), and hexa(peri)benzocoronene (C42H18) in the 3–100 μm region. Apart from providing experimental spectra that can be compared directly to astronomical data, such IR spectra are crucial for assessing the accuracy of theoretically predicted spectra used to interpret interstellar IR emission. Here we use the experimental spectra to evaluate the performance of conventional calculations using the harmonic approximation, as well as calculations with an anharmonic (GVPT2) treatment. The harmonic prediction agrees well with the experiment between 100 and 1000 cm−1 (100 and 10 μm) but shows significant shortcomings in the combination band (1600–2000 cm−1, 6.25–5 μm) and CH-stretch (2950–3150 cm−1, 3.4–3.17 μm) regions. Especially the CH-stretch region is known to be dominated by the effects of anharmonicity, and we find that large PAHs are no exception. However, for the CH out-of-plane region (667–1000 cm−1, 15–10 μm) the anharmonic treatment that significantly improves the predicted spectra for small PAHs leads to large and unrealistic frequency shifts, and intensity changes for large PAHs, thereby rendering the default results unreliable. A detailed analysis of the results of the anharmonic treatment suggests a possible route for improvement, although the underlying cause for the large deviations remains a challenge for theory.

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Crofton, Mark W., Welf A. Kreiner, Mary‐Frances Jagod, Brent D. Rehfuss, and Takeshi Oka. "Observation of the infrared spectrum of methyl cation CH+3." Journal of Chemical Physics 83, no. 7 (October 1985): 3702–3. http://dx.doi.org/10.1063/1.449125.

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25

Nishida, Jun, Shinsuke Shigeto, Sohshi Yabumoto, and Hiro-o. Hamaguchi. "Anharmonic coupling of the CH-stretch and CH-bend vibrations of chloroform as studied by near-infrared electroabsorption spectroscopy." Journal of Chemical Physics 137, no. 23 (December 21, 2012): 234501. http://dx.doi.org/10.1063/1.4770264.

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26

Hashimoto, Mamoru, and Hiro-O. Hamaguchi. "Real-Time Pursuit of Crystal Growth by Millisecond Time-Resolved Multichannel Fourier Transform Infrared Spectroscopy." Applied Spectroscopy 52, no. 2 (February 1998): 222–25. http://dx.doi.org/10.1366/0003702981943536.

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The surface (about 130 molecular layers) of an oriented thin crystal of decanoic acid was subjected to sudden melting by a laser-induced temperature jump (T-jump), and the process of subsequent crystal re-growth was monitored by millisecond time-resolved multichannel Fourier transform infrared spectroscopy. The gauche–trans structural change of the alkane part of the molecule has been probed by the CH stretch bands in the 2800–3000 cm−1 region. The change in the molecular orientation has been detected by the OH stretch band around 3065 cm−1. The recovery curves for the CH2 antisymmetric stretch and the OH stretch bands are markedly different from each other in the first 200 ms, suggesting that the gauche–trans structural changes precedes the crystal re-growth. After 500 ms, the recovery curves become identical. This result means that the rate of the gauche to the trans structural change is equal to the rate of the recovery of the molecular orientation. It is highly likely that a fast equilibrium is attained between the gauche and the trans conformations in the liquid phase after 500 ms from the sudden melting and that the crystal re-growth takes place solely via the all-trans structure in the liquid phase.

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27

Vijayakumar, S., R. Arulkumaran, R. Sundararajan, S. P. Sakthinathan, R. Suresh, D. Kamalakkannan, K. Ranganathan, et al. "Microwave Assisted Synthesis, Spectral Studies and Antimicrobial Activities of some 2′,4′-Difluorophenyl Chalcones." International Letters of Chemistry, Physics and Astronomy 14 (September 2013): 68–86. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.14.68.

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Some 2′,4′-difluorophenyl chalcones have been synthesized under microwave irradiation using aldol condensation between 2,4-difluoroacetophenone and substituted benzaldehydes using catalytic amount of hydroxyapatite. The yields of the chalcones are more than 85%. The purities of these synthesized chalcones were examined by their physical constants and spectroscopic data. The UV absorption maxima (λmax, nm), infrared stretches (ν, cm-1) of CO, fingerprint region of CHip/op, CH=CHop, C=Cop modes, NMR chemical shifts (δ, ppm) of vinyl proton, carbon and carbonyl carbons have been assigned and correlated with Hammett substituent constants, F and R parameters using single and multi-regression analysis. From the statistical analysis the effect of substituent on the above spectral frequencies can be discussed. The antimicrobial activities of these synthesized chalcones have been screened using Bauer-Kirby method.

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28

Vijayakumar, S., R. Arulkumaran, R. Sundararajan, S. P. Sakthinathan, R. Suresh, D. Kamalakkannan, K. Ranganathan, et al. "Microwave Assisted Synthesis, Spectral Studies and Antimicrobial Activities of some 2′,4′-Difluorophenyl Chalcones." International Letters of Chemistry, Physics and Astronomy 14 (May 19, 2013): 68–86. http://dx.doi.org/10.56431/p-v23467.

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Some 2′,4′-difluorophenyl chalcones have been synthesized under microwave irradiation using aldol condensation between 2,4-difluoroacetophenone and substituted benzaldehydes using catalytic amount of hydroxyapatite. The yields of the chalcones are more than 85%. The purities of these synthesized chalcones were examined by their physical constants and spectroscopic data. The UV absorption maxima (λmax, nm), infrared stretches (ν, cm-1) of CO, fingerprint region of CHip/op, CH=CHop, C=Cop modes, NMR chemical shifts (δ, ppm) of vinyl proton, carbon and carbonyl carbons have been assigned and correlated with Hammett substituent constants, F and R parameters using single and multi-regression analysis. From the statistical analysis the effect of substituent on the above spectral frequencies can be discussed. The antimicrobial activities of these synthesized chalcones have been screened using Bauer-Kirby method.

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29

Han, Jiaxiang, Shuiming Hu, Hongbing Chen, Yurii Utkin, John M. Brown, and Robert F. Curl. "Jet-cooled infrared spectrum of methoxy in the CH stretching region." Physical Chemistry Chemical Physics 9, no. 28 (2007): 3725. http://dx.doi.org/10.1039/b700502d.

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30

Papanastasiou, Dimitrios K., François Bernard, and James B. Burkholder. "Trimethylchlorosilane, (CH 3 ) 3 SiCl: OH reaction kinetics and infrared spectrum." International Journal of Chemical Kinetics 52, no. 4 (January 21, 2020): 221–26. http://dx.doi.org/10.1002/kin.21344.

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31

Rashev, S. "A tier model calculation of the absorption spectrum of the fourth CH stretch overtone state CH(v=5) in benzene." Chemical Physics Letters 312, no. 5-6 (October 1999): 561–66. http://dx.doi.org/10.1016/s0009-2614(99)01006-4.

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32

Callegari, A., H. K. Srivastava, U. Merker, K. K. Lehmann, G. Scoles, and M. J. Davis. "Eigenstate resolved infrared–infrared double-resonance study of intramolecular vibrational relaxation in benzene: First overtone of the CH stretch." Journal of Chemical Physics 106, no. 1 (January 1997): 432–35. http://dx.doi.org/10.1063/1.473205.

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33

York, D. G., J. Dahlstrom, D. E. Welty, T. Oka, L. M. Hobbs, S. Johnson, S. D. Friedman, et al. "Anomalously Broad Diffuse Interstellar Bands and Excited CH+ Absorption in the Spectrum of Herschel 36." Proceedings of the International Astronomical Union 9, S297 (May 2013): 89–93. http://dx.doi.org/10.1017/s1743921313015639.

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AbstractAnomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, an O star system next to the bright Hourglass nebula of the Hii region Messier 8. Excited lines of CH and CH+ are seen as well. We show that the region is very compact and itemize other anomalies of the gas. An infrared-bright star within 400 AU is noted. The combination of these effects produces anomalous DIBs, interpreted by Oka et al. (2013, see also this volume) as being caused predominantly by infrared pumping of rotational levels of relatively small molecules.

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34

Franke, Peter R., Daniel P. Tabor, Christopher P. Moradi, Gary E. Douberly, Jay Agarwal, Henry F. Schaefer, and Edwin L. Sibert. "Infrared laser spectroscopy of the n-propyl and i-propyl radicals: Stretch-bend Fermi coupling in the alkyl CH stretch region." Journal of Chemical Physics 145, no. 22 (December 14, 2016): 224304. http://dx.doi.org/10.1063/1.4971239.

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35

Jian, Hung-Yang, Chih-Tsun Yang, and Li-Kang Chu. "Gaseous infrared spectra of the simplest geminal diol CH2(OH)2 and the isotopic analogues in the hydration of formaldehyde." Physical Chemistry Chemical Physics 23, no. 27 (2021): 14699–705. http://dx.doi.org/10.1039/d1cp01354h.

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36

Chen, Mingzhe, and Jinming Xu. "CO2 Capture Mechanism by Deep Eutectic Solvents Formed by Choline Prolinate and Ethylene Glycol." Molecules 28, no. 14 (July 17, 2023): 5461. http://dx.doi.org/10.3390/molecules28145461.

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The choline prolinate ([Ch][Pro]) as a hydrogen bond acceptor and ethylene glycol (EG) as a hydrogen bond donor are both used to synthesize the deep eutectic solvents (DESs) [Ch][Pro]-EG to capture CO2. The CO2 capacity of [Ch][Pro]-EG is determined, and the nuclear magnetic resonance (NMR) and infrared (IR) spectrum are used to investigate the CO2 capture mechanism. The results indicate that CO2 reacts with both the amino group of [Pro]− anion and the hydroxyl group of EG, and the mechanism found in this work is different from that reported in the literature for the [Ch][Pro]-EG DESs.

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37

Sauval, A. J., and N. Grevesse. "The Sun as a Laboratory Source for IR Molecular Spectroscopy." Symposium - International Astronomical Union 154 (1994): 549–54. http://dx.doi.org/10.1017/s0074180900124842.

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The infrared solar spectrum is used to refine our knowledge of molecular constants of CH and CO and to test the accuracy of transition probabilities and dissociation energies of a few diatomic molecules.

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38

Chan, Ya-Chu, Andrew Kortyna, and David J. Nesbitt. "High-resolution infrared spectroscopy of supersonically cooled singlet carbenes: Bromomethylene (HCBr) in the CH stretch region." Journal of Chemical Physics 156, no. 1 (January 7, 2022): 014304. http://dx.doi.org/10.1063/5.0077341.

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39

Ahmed, M. Khalique, Michael P. McLeod, Jean Nézivar, and Allison W. Giuliani. "Fourier transform infrared and near-infrared spectroscopic methods for the detection of toxic Diethylene Glycol (DEG) contaminant in glycerin based cough syrup." Spectroscopy 24, no. 6 (2010): 601–8. http://dx.doi.org/10.1155/2010/608749.

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Recently there have been reports of the contamination of cough syrups with Diethylene Glycol (DEG). The consumption of such cough syrups has devastating effects on the health. In this paper we report evidence that Fourier transform infrared (FT-IR) and near-infrared (NIR) spectroscopic techniques are viable, simple, cost effective, rapid and fool proof methods for the identification and quantification of DEG in glycerin based cough syrups. The FT-IR and NIR spectra of the glycerin based cough syrup and up to 50:50 mixtures of DEG in cough syrup are recorded. The major peaks in the FT-IR spectrum of the cough syrup are assigned to the OH stretching (∼3300 cm−1), CH stretching (∼2900 cm−1), CH bending (1500–1200 cm−1) and C–O stretching (1200–900 cm−1) vibrational modes. In the FT-IR spectra of the mixtures, DEG contribute distinct peaks due to the vibrations of the C–O (920 cm−1) and OC2H4(892 cm−1) moieties of its backbone and form the basis of the DEG detection and quantification. The prominent peaks of the NIR spectra of cough syrup and DEG are assigned to the first overtones of OH and CH, and to the combination of OH and CH fundamental vibrations. Both FT-IR and NIR Partial Least Square (PLS) calibrations produced correlation coefficients of 0.98.

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40

DeSain, J. D., R. I. Thompson, S. D. Sharma, and R. F. Curl. "The rotationally resolved infrared spectrum of the ν1 stretch of the allyl radical." Journal of Chemical Physics 109, no. 18 (November 8, 1998): 7803–9. http://dx.doi.org/10.1063/1.477426.

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41

WU, GEFEI, M. KALTCHEV, and W. T. TYSOE. "THE KINETICS AND INFRARED SPECTROSCOPY OF C1 HYDROCARBONS ADSORBED ON CLEAN AND OXYGEN-MODIFIED Mo(100)." Surface Review and Letters 06, no. 01 (February 1999): 13–21. http://dx.doi.org/10.1142/s0218625x99000044.

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The surface infrared spectra (700–2300 cm -1) of CH 3 I , CD 3 I , CH 2 I 2 and CD 2 I 2 adsorbed on Mo(100) at 80 K have been observed and assigned. The strongest infrared absorption of CH 3 I is the δs( CH 3) mode at 1236 cm -1, which shifts significantly on heating the surface to 135 K, yielding a new peak at 1106 cm -1 indicating the formation of a surface- CH 3 species. This new feature dominates the spectrum after annealing to 160 K and disappears at 235 K, where the TPD results show the desorption of methane. This chemistry was also studied on oxygen-covered Mo(100) with oxygen coverages of 1.0 and 1.5. These were not found to substantially affect the surface chemistry. When CH 2 I 2 is adsorbed on Mo(100), the ω( CH 2) mode at 1107 cm -1 is the strongest feature, and when one heats the sample to 135 K, a new peak appears at 1061 cm -1 which is ascribed to the formation of a surface- CH 2 I species. This peak disappears on heating at about 200 K, where previous ultraviolet-photoelectron-spectroscopic data showed the formation of a surface- C 1 species. No RAIRS data have been reported for adsorbed-methylene species, because of either a low-adsorption cross section or the lack of appropriate symmetry of these modes. The deuterated molecules show the same effects except that peaks are shifted as expected so that ν(H)/ν(D) ~1.35.

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42

Utkin, Yu G., Jia-Xiang Han, Fuge Sun, Hong-Bing Chen, Graham Scott, and R. F. Curl. "High-resolution jet-cooled and room temperature infrared spectra of the ν3 CH stretch of vinoxy radical." Journal of Chemical Physics 118, no. 23 (June 15, 2003): 10470–76. http://dx.doi.org/10.1063/1.1573634.

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43

Xu, Li-Hong, Xiaoliang Wang, Thomas J. Cronin, David S. Perry, Gerald T. Fraser, and Alan S. Pine. "Sub-Doppler Infrared Spectra and Torsion–Rotation Energy Manifold of Methanol in the CH-Stretch Fundamental Region." Journal of Molecular Spectroscopy 185, no. 1 (September 1997): 158–72. http://dx.doi.org/10.1006/jmsp.1997.7367.

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44

Dawadi, Mahesh B., C. Michael Lindsay, Andrei Chirokolava, David S. Perry, and Li-Hong Xu. "Novel patterns of torsion-inversion-rotation energy levels in the ν11 asymmetric CH-stretch spectrum of methylamine." Journal of Chemical Physics 138, no. 10 (March 14, 2013): 104305. http://dx.doi.org/10.1063/1.4794157.

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45

Davies, Julia A., Shengfu Yang, and Andrew M. Ellis. "Infrared spectra of carbocations and CH₄⁺ in helium." Physical Chemistry Chemical Physics 23, no. 48 (2021): 27449–59. http://dx.doi.org/10.1039/d1cp03138d.

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Infrared (IR) spectra of rigid and fluxional carbocations have been measured at low temperatures (≤10 K) following electron ionization of superfluid helium nanodroplets doped with methane, and an IR spectrum for CH4+ is presented for the first time.

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46

Maechling, C. R., D. A. V. Kliner, and D. Klenerman. "Sum Frequency Spectra in the C-H Stretch Region of Adsorbates on Iron." Applied Spectroscopy 47, no. 2 (February 1993): 167–72. http://dx.doi.org/10.1366/0003702934048361.

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Infrared-visible sum frequency generation (SFG) was used to record vibrational spectra in the C-H stretch region of single monolayer Langmuir-Blodgett films of stearic acid, octadecylamine, and p-octadecylphenyl acetic acid on iron oxide, demonstrating the sensitivity of SFG to about 0.1 monolayer. Within our present signal-to-noise limitations, it was not possible to obtain SFG spectra of the aromatic C-H stretch in p-octadecylphenyl acetic acid or the N-H stretch in octadecylamine. Vibrational spectra in the C-H stretch region have also been obtained for chemically adsorbed monolayers of stearic acid and oleic imidazoline on iron oxide; however an undetermined fraction of these spectra result from hydrocarbon contamination. Finally, an SFG spectrum was obtained at a buried interface, that of p-octadecylphenyl acetic acid on iron oxide under water. The potential of SFG as a surface analytical tool is discussed.

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47

McIlroy, Andrew, and David J. Nesbitt. "High‐resolution, slit jet infrared spectroscopy of hydrocarbons: Quantum state specific mode mixing in CH stretch‐excited propyne." Journal of Chemical Physics 91, no. 1 (July 1989): 104–13. http://dx.doi.org/10.1063/1.457496.

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48

Dréan, P., H. Bürger, J. Demaison, and J. E. Boggs. "Structure, ab initio harmonic force field and infrared spectrum of CH 3 C As." Journal of Molecular Structure 485-486 (August 1999): 51–56. http://dx.doi.org/10.1016/s0022-2860(99)00041-1.

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49

Davidson, Steven A., Kenneth M. Evenson, and John M. Brown. "A Measurement of the Rotational Spectrum of the CH Radical in the Far‐Infrared." Astrophysical Journal 546, no. 1 (January 2001): 330–37. http://dx.doi.org/10.1086/318255.

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50

Davies, A. M. C., and Sheridan G. Rutland. "Identification of an OH, CH combination band in the near infrared spectrum of ethanol." Spectrochimica Acta Part A: Molecular Spectroscopy 44, no. 11 (January 1988): 1143–45. http://dx.doi.org/10.1016/0584-8539(88)80085-0.

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