Photodissociation Dynamics of Acetic Acid and Trifluoroacetic Acid at 193 nm

Abstract

Photodissociation dynamics of acetic acid and trifluoroacetic acid at 193 nm have been investigated by measuring laser-induced fluorescence spectra of OH fragments. The OH fragments are produced exclusively in the ground electronic state. The measured energy distributions among the fragments are fr(OH) = 0.05, ft = 0.42, fint(Ac) = 0.53 and fr(OH) = 0.05, ft = 0.33, and fint(FAc) = 0.62, for acetic and trifluoroacetic acid, respectively, and negligible vibrational excitation in the OH fragments was observed. The dissociation does not depend on the polarization of the dissociating light. It was concluded from the measured energy distribution and no polarization dependence that the electronic transition at 193 nm leads the parent molecule to the singlet excited surface, and the dissociation takes place along the triplet surface with an exit channel barrier. From the estimated internal energies in the acetyl radicals, the lifetimes of the acetyl radicals are estimated from the RRKM theory.