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Title: Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy

Abstract

Following the photodissociation of o-fluorotoluene [o-C{sub 6}H{sub 4}(CH{sub 3})F] at 193 nm, rotationally resolved emission spectra of HF(1{<=}v{<=}4) in the spectral region of 2800-4000 cm{sup -1} are detected with a step-scan Fourier transform spectrometer. HF(v{<=}4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature {approx}1080 K; a short extrapolation from data in the period of 0.5-4.5 {mu}s leads to a nascent rotational temperature of 1130{+-}100 K with an average rotational energy of 9{+-}2 kJ mol{sup -1}. The observed vibrational distribution of (v=1):(v=2):(v=3)=67.6: 23.2: 9.2 corresponds to a vibrational temperature of 5330{+-}270 K. An average vibrational energy of 25{+-}{sub 3}{sup 12} kJ mol{sup -1} is derived based on the observed population of HF(1{<=}v{<=}3) and estimates of the population of HF (v=0 and 4) by extrapolation. Experiments performed on p-fluorotoluene [p-C{sub 6}H{sub 4}(CH{sub 3})F] yielded similar results with an average rotational energy of 9{+-}2 kJ mol{sup -1} and vibrational energy of 26{+-}{sub 3}{sup 12} kJ mol{sup -1} for HF. The observed distributions of internal energy of HF in both cases are consistent with that expected for four-center elimination. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF.more » An observed vibrational energy of HF produced from fluorotoluene slightly smaller than that from fluorobenzene might indicate the involvement of seven-membered-ring isomers upon photolysis.« less

Authors:
; ; ;  [1];  [2];  [2]
  1. Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan (China)
  2. (China)
Publication Date:
OSTI Identifier:
20723267
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 123; Journal Issue: 22; Other Information: DOI: 10.1063/1.2131072; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CHEMICAL BONDS; EMISSION SPECTRA; EXTRAPOLATION; FOURIER TRANSFORM SPECTROMETERS; FOURIER TRANSFORMATION; HYDROFLUORIC ACID; ISOMERS; LUMINESCENCE; ORGANIC FLUORINE COMPOUNDS; PHOTOLYSIS; PHOTON-MOLECULE COLLISIONS; ROTATIONAL STATES; TIME RESOLUTION; VIBRATIONAL STATES

Citation Formats

Yang, S.-K., Liu, S.-Y., Chen, H.-F., Lee, Y.-P., Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan, and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan. Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy. United States: N. p., 2005. Web. doi:10.1063/1.2131072.
Yang, S.-K., Liu, S.-Y., Chen, H.-F., Lee, Y.-P., Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan, & Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan. Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy. United States. doi:10.1063/1.2131072.
Yang, S.-K., Liu, S.-Y., Chen, H.-F., Lee, Y.-P., Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan, and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan. Thu . "Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy". United States. doi:10.1063/1.2131072.
@article{osti_20723267,
title = {Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy},
author = {Yang, S.-K. and Liu, S.-Y. and Chen, H.-F. and Lee, Y.-P. and Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan},
abstractNote = {Following the photodissociation of o-fluorotoluene [o-C{sub 6}H{sub 4}(CH{sub 3})F] at 193 nm, rotationally resolved emission spectra of HF(1{<=}v{<=}4) in the spectral region of 2800-4000 cm{sup -1} are detected with a step-scan Fourier transform spectrometer. HF(v{<=}4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature {approx}1080 K; a short extrapolation from data in the period of 0.5-4.5 {mu}s leads to a nascent rotational temperature of 1130{+-}100 K with an average rotational energy of 9{+-}2 kJ mol{sup -1}. The observed vibrational distribution of (v=1):(v=2):(v=3)=67.6: 23.2: 9.2 corresponds to a vibrational temperature of 5330{+-}270 K. An average vibrational energy of 25{+-}{sub 3}{sup 12} kJ mol{sup -1} is derived based on the observed population of HF(1{<=}v{<=}3) and estimates of the population of HF (v=0 and 4) by extrapolation. Experiments performed on p-fluorotoluene [p-C{sub 6}H{sub 4}(CH{sub 3})F] yielded similar results with an average rotational energy of 9{+-}2 kJ mol{sup -1} and vibrational energy of 26{+-}{sub 3}{sup 12} kJ mol{sup -1} for HF. The observed distributions of internal energy of HF in both cases are consistent with that expected for four-center elimination. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. An observed vibrational energy of HF produced from fluorotoluene slightly smaller than that from fluorobenzene might indicate the involvement of seven-membered-ring isomers upon photolysis.},
doi = {10.1063/1.2131072},
journal = {Journal of Chemical Physics},
number = 22,
volume = 123,
place = {United States},
year = {Thu Dec 08 00:00:00 EST 2005},
month = {Thu Dec 08 00:00:00 EST 2005}
}
  • Following photodissociation of 2-chloropropene (H{sub 2}CCClCH{sub 3}) at 193 nm, vibration-rotationally resolved emission spectra of HCl ({upsilon}{<=}6) in the spectral region of 1900-2900 cm{sup -1} were recorded with a step-scan time-resolved Fourier-transform spectrometer. All vibrational levels show a small low-J component corresponding to {approx}400 K and a major high-J component corresponding to 7100-18 700 K with average rotational energy of 39{+-}{sub 3}{sup 11} kJ mol{sup -1}. The vibrational population of HCl is inverted at {upsilon}=2, and the average vibrational energy is 86{+-}5 kJ mol{sup -1}. Two possible channels of molecular elimination producing HCl+propyne or HCl+allene cannot be distinguished positively basedmore » on the observed internal energy distribution of HCl. The observed rotational distributions fit qualitatively with the distributions of both channels obtained with quasiclassical trajectories (QCTs), but the QCT calculations predict negligible populations for states at small J. The observed vibrational distribution agrees satisfactorily with the total QCT distribution obtained as a weighted sum of contributions from both four-center elimination channels. Internal energy distributions of HCl from 2-chloropropene and vinyl chloride are compared.« less
  • We report on the photodissociation dynamics study of n-butyl nitrite and isoamyl nitrite by means of time-resolved Fourier transform infrared (TR-FTIR) emission spectroscopy. The obtained TR-FTIR emission spectra of the nascent NO fragments produced in the 355 nm laser photolysis of the two alkyl nitrite species showed an almost identical rotational temperature and vibrational distributions of NO. In addition, a close resemblance between the two species was also found in the measured temporal profiles of the IR emission of NO and the recorded UV absorption spectra. The experimental results are consistent with our ab initio calculations using the time-dependent densitymore » functional theory at the B3LYP/6-311G(d,p) level, which indicate that the substitution of one of the two {gamma}-H atoms in n-C{sub 4}H{sub 9}ONO with a methyl group to form (CH{sub 3}){sub 2}C{sub 3}H{sub 5}ONO has only a minor effect on the photodissociation dynamics of the two molecules.« less
  • The product state distributions for hot atom collisions of H(D) with HF(DF) with a broad range of collision energies between 1.2 eV and 2.3eV are measured with time-resolved Fourier transform spectroscopy and rotational resolution under multiple collision conditions. In most cases the vibrational distributions of reactive and nonreactive channels can be distinguished. All rotational distributions have a similar appearance with a maximum at J=5 and an additional pronounced higher component, which cannot be described by a single Boltzmann distribution. The results are compared with recent three dimensional quasiclassical trajectory calculations (accompanying paper by Schatz) by applying a multiple collision modelmore » for both the H(D) atom slowdown and the rotational and vibrational relaxation. The rotational distributions can also be interpreted by a three dimensional asymmetric breathing ellipsoid model. {copyright} {ital 1997 American Institute of Physics.}« less
  • Time-resolved Fourier transform infrared (FTIR) emission is used to study the formation of CCH in the photodissociation of C/sub 2/H/sub 2/ at 193 nm. Excitation of C/sub 2/H/sub 2/ at 193 nm is known to populate the 10..nu../sub 3/ level of the trans--bent electronically excited state of acetylene, which undergoes decomposition. State-resolved infrared emission is obtained from the CCH radicals that are produced. Only vibronic levels which originate or borrow oscillator strength from the low-lying electronically excited state of CCH, A-italic-tilde /sup 2/Pi, are observed in this study. The relative intensities of these bands are measured and the rotational statemore » distribution for the A-italic-tilde(010) state is obtained. The observed average rotational energy of CCH is approx.156 cm/sup -1/, which is less than the average rotational energy of the acetylene precursor. A kinematic model which can account for a rotational cooling effect in the A-italic-tilde(010) state is described. The model incorporates the angular momentum generated by the impulsive kick due to the release of the H atom and the cooling due to the orbital angular momentum carried away by the tangential velocity of the H atom, which is imparted by the initial C/sub 2/H/sub 2/ rotation.« less
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