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

Journal Article · Thu Dec 08 04:00:00 EST 2005 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2131072· OSTI ID:20723267

Yang, S -K; Liu, S -Y; Chen, H -F; Lee, Y -P ^[1]

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1. Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

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.

• OSTI ID: 20723267
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 22 Vol. 123; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

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