Dynamics of H Atom Production from Photodissociation of Formic Acid at 205 nm

摘要

Chemistry of formic acid (HCOOH) is of fundamental interest because it is an important intermediate in oxidation of unsaturated hydrocarbons in combustion and the most abundant organic pollutant in Earth's atmosphere. Structures and dynamics of formic acid in the excited electronic states are of special importance in understanding atmospheric chemistry. In UV, the absorption spectrum shows some vibrational structures superimposed by continuous absorption starting from about 250 nm, which is assigned as the n → π*_(C=O) electronic transition typical for simple carbonyl compounds. The structures in this band are long progressions of the C=O stretching (V3) and the O-C-O bending (V7) vibrations resulting from structural changes from the planar to the pyramidal structure upon electronic transition due to molecular orbital interactions mentioned by Walsh. Since the transition is vibronically allowed through V3 and v7, the direction of transition dipole moment has all three components in space expecting isotropic velocity distribution of fragments upon photodissociation.