Overtone-Induced Chemistry of Trifluoroacetic Acid: An Experimental and Theoretical Study

Abstract

The effect of overtone-induced chemistry on the atmospheric fate of trifluoroacetic acid has been investigated. We report the absolute absorption intensities for the vOH = 3, 4, and 5 overtone transitions as well as an ab initio calculation of the energetics of the dissociation pathways. Calculations at the MP2 level give the lowest dissociation barrier as 50.3 kcal mol-1 for the elimination of HF. Integrated cross sections for vOH = 3, 4, and 5 are 2.70 × 10-20, 1.68 × 10-21, and 1.5 × 10-22 cm2 molecule-1 cm-1, respectively. Dissociation may proceed after absorption into v = 5 or 6, giving an upper limit to the photodissociation rate constants of 3.7 × 10-9 s-1 or 2.5 × 10-10 s-1, respectively. These correspond to a tropospheric lifetime of between 8 and 127 years. The overtone-driven photodissociation is more important than the ultraviolet photodissociation in the troposphere but is insignificant in comparison to wet deposition and the reaction with OH radicals.