Isotopic substitution effects on acetic acid photofragmentation dynamics

The internal and translational energy distributions of the OD X 2Π photofragment resulting from the 218 nm photolysis of acetic acid-d are presented. Comparison of these results with those of acetic acid-h photolysis reveals the effects of isotopic substitution on the α-cleavage photodynamics of 1(n, π∗)-excited acetic acid. The OD product contains only approximately 17% more rotational energy than the corresponding OH fragment, and the OD translational energy distributions broaden with increasing fragment rotational level. A pure impulsive model for the dissociation dynamics is inadequate to explain these results. Interpretations which also include contributions from excited state bending motions may be more realistic.