Photodissociation and photoisomerization of {alpha}-fluorotoluene and 4-fluorotoluene in a molecular beam

Journal Article · Sat Oct 07 04:00:00 EDT 2006 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2219445· OSTI ID:20864301

Huang, C -L; Jiang, J -C; Dyakov, Yuri A; Lin, M -F; Tseng, C -M; Lin, S H; Lee, Yuan T; Ni, C -K ^[1]

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1. 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, Journal Name: Journal of Chemical Physics Journal Issue: 13 Vol. 125; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
BRANCHING RATIO
DISSOCIATION
ELECTRONS
FAR ULTRAVIOLET RADIATION
HYDROFLUORIC ACID
ISOMERIZATION
ISOMERS
MOLECULAR BEAMS
ORGANIC FLUORINE COMPOUNDS
PHOTOCHEMISTRY
PHOTOIONIZATION
PHOTOLYSIS
REACTION KINETICS
SPECTROSCOPY
TOLUENE