Isotope effects in the ultrafast photodissociation of acetone 3s Rydberg state excited at 195Â nm

The deuterium isotope effect in the photodissociation of acetone S2 state was studied using femtosecond pump-probe ionization spectroscopy. The transients obtained for both isotopomers can be well described by the same mechanism in which the primary dissociation occurs on the S1 surface. Substantial isotope effects were observed in every stage of the reaction. Our results indicted that upon full deuteration the initial-state decay from S2 to S1 slows down by a factor of three, the subsequent adiabatic dissociation on the S1 surface slows down by a factor of four, and the secondary dissociation slows down by a factor of ∼1.6.