Photodissociation of acetone revisited: Femtosecond transient absorption of S1 state and highly excited Rydberg state in the gas phase

Abstract

AbstractPhotodissociation dynamics of acetone in gas phase were, for the first time, investigated using the pump‐probe technique of femtosecond transient absorption. To obtain a genuine time profile of nR state, we employed 200‐nm and 400‐nm pulses for two‐photon excitation and three‐photon excitation, respectively. In gas phase of acetone, the extraordinarily stable nR state originated from nR states in the Franck–Condon region, whose decay time constant was 350 ± 10 fs, was observed after excitation by three‐photon absorption of 400‐nm pulses. In the low‐power case of 267 nm, the photodissociation dynamics in the S1 state by one‐photon absorption showed that acetone was completely dissociated into two methyl radicals and C=O via an acetyl radical intermediate with a lifetime of 200 ± 10 fs. In the high‐power case of 267‐nm light, we interpreted the transient, although this is a subject of ongoing debate, as caused by both the photodissociation dynamics of the S1 state for a fast component and the dynamics of nR states for long‐lived species.