Ketone excited state lifetimes measured by deep UV ultrafast photoionization spectroscopy

Ultrafast photoionization spectroscopy has been used to measure excited state lifetimes for several ketones excited near 193 nm. The decay times for aliphatic ketones are between 2 and 9 ps, which are consistent with 3s Rydberg state predissociation and are similar to previously reported results for acetone. The lifetimes of cyclic ketones are somewhat longer than for acyclic ones, which is attributed to predissociation promoted by internal rotation for the latter. The aromatic ketone acetophenone dissociates more quickly, probably because of rapid intersystem crossing and/or interaction with a valence state that lies in this spectral region as a result of delocalization.