Gas phase dynamics of triplet formation in benzophenone

Abstract

Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S₂ to the final decay of T₁ to the ground state S₀. We have found that the triplet formation can be described almost as a direct process in preparing T₁, the lowest reacting triplet state, from the S₁ state after S₂ → S₁ internal conversion. The molecule was also deposited by a pick-up technique on cold argon clusters providing a soft relaxation medium without evaporation of the molecule and the mechanism was identical. This cluster technique is a model for medium influenced electronic relaxation and provides a continuous transition from the isolated gas phase to the relaxation dynamics in solution.