Photodissociation and photoisomerization of {alpha}-fluorotoluene and 4-fluorotoluene in a molecular beam
- Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 10617 (China)
The photodissociation of jet-cooled {alpha}-fluorotoluene and 4-fluorotoluene at 193 and 248 nm was studied using vacuum ultraviolet (vuv) photoionization/multimass ion imaging techniques as well as electron impact ionization/photofragment translational spectroscopy. Four dissociation channels were observed for {alpha}-fluorotoluene at both 193 and 248 nm, including two major channels C{sub 6}H{sub 5}CH{sub 2}F{yields}C{sub 6}H{sub 5}CH{sub 2} (or C{sub 7}H{sub 7})+F and C{sub 6}H{sub 5}CH{sub 2}F{yields}C{sub 6}H{sub 5}CH (or C{sub 7}H{sub 6})+HF and two minor channels C{sub 6}H{sub 5}CH{sub 2}F{yields}C{sub 6}H{sub 5}CHF+H and C{sub 6}H{sub 5}CH{sub 2}F{yields}C{sub 6}H{sub 5}+CH{sub 2}F. The vuv wavelength dependence of the C{sub 7}H{sub 7} fragment photoionization spectra indicates that at least part of the F atom elimination channel results from the isomerization of {alpha}-fluorotoluene to a seven-membered ring prior to dissociation. Dissociation channels of 4-fluorotoluene at 193 nm include two major channels C{sub 6}H{sub 4}FCH{sub 3}{yields}C{sub 6}H{sub 4}FCH{sub 2}+H and C{sub 6}H{sub 4}FCH{sub 3}{yields}C{sub 6}H{sub 4}F+CH{sub 3} and two minor channels C{sub 6}H{sub 4}FCH{sub 3}{yields}C{sub 6}H{sub 5}CH{sub 2} (or C{sub 7}H{sub 7})+F and C{sub 6}H{sub 4}FCH{sub 3}{yields}C{sub 6}H{sub 5}CH (or C{sub 7}H{sub 6})+HF. The dissociation rates for {alpha}-fluorotoluene at 193 and 248 nm are 3.3x10{sup 7} and 5.6x10{sup 5} s{sup -1}, respectively. The dissociation rate for 4-fluorotoluene at 193 nm is 1.0x10{sup 6} s{sup -1}. An ab initio calculation demonstrates that the barrier height for isomerization from {alpha}-fluorotoluene to a seven-membered ring isomer is much lower than that from 4-fluorotoluene to a seven-membered ring isomer. The experimental observed differences of dissociation rates and relative branching ratios between {alpha}-fluorotoluene and 4-fluorotoluene may be explained by the differences in the six-membered ring to seven-membered ring isomerization barrier heights, F atom elimination threshold, and HF elimination threshold between {alpha}-fluorotoluene and 4-fluorotoluene.
- OSTI ID:
- 20864301
- Journal Information:
- Journal of Chemical Physics, Vol. 125, Issue 13; Other Information: DOI: 10.1063/1.2219445; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
Similar Records
Photodissociation dynamics of pyrimidine
Energy partitioning in elementary gas phase reactions: Progress report, March 1, 1986--August 31, 1988