Review: Photodissociation and Photoisomerization of Small Aromatic Molecules in a Molecular Beam

Abstract

The photodissociation and photoisomerization of (D₃)toluene, (D₆)m-xylene, 4-fluorotoluene, α−fluorotoluene, and α,α,α-trifluorotoluene in a molecular beam at 248 and 193 nm were studied by multimass ion imaging techniques. The dissociation channels, dissociation rates, and photofragment translational-energy distributions were obtained. A new isomerization pathway, from a six- to a seven-membered ring followed by rearomatization prior to dissociation, was observed for toluene and xylene after photonic exitation at 193 nm. This isomerization is significant as the carbon and hydrogen atoms of the methyl group are involved in an exchange with the atoms in the aromatic ring during the process. This complete isomerization was not observed for 4-fluorotoluene, α-fluorotoluene and α,α,α-trifluorotoluene. The dissociation rate of toluene at 248 nm is too slow to be measured, and the upper limit of the dissociation rates at 248 nm is estimated to be 10⁴s^–1.

Manuscript received: 1 October 2001.

Final version: 29 November 2001.