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

Sheng Kai Yang, Suet Yi Liu, Hui Fen Chen, Yuan-Pern Lee*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Following the photodissociation of o -fluorotoluene [o- C6 H4 (CH3) F] at 193 nm, rotationally resolved emission spectra of HF (1≤v≤4) in the spectral region of 2800-4000 cm-1 are detected with a step-scan Fourier transform spectrometer. HF (v≤4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature ∼1080 K; a short extrapolation from data in the period of 0.5-4.5 μs leads to a nascent rotational temperature of 1130±100 K with an average rotational energy of 9±2 kJ mol-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 ±312 kJ mol-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- C6 H4 (C H3) F] yielded similar results with an average rotational energy of 9±2 kJ mol-1 and vibrational energy of 26 ±312 kJ mol-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.

Original languageEnglish
Article number224304
JournalJournal of Chemical Physics
Volume123
Issue number22
DOIs
StatePublished - 27 Dec 2005

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