Non-adiabatic effects in chemistry revealed by time-resolved charged-particle imaging

Abstract

Recent advances in photoelectron and photoion imaging techniques are reviewed. The general background to photofragmentation spectroscopy and, in particular, the information that can be extracted from laboratory and molecular frame photoproduct angular distributions are briefly discussed. Recent technological advances to the photofragment imaging experiment first introduced by Chandler and Houston, such as velocity mapping and event counting, are also described. The main focus of the review is devoted to time-resolved imaging applications in which femtosecond pump?probe techniques are combined with charged particle imaging. We survey the recent literature and describe a number of applications; in particular we show how pump?probe photoelectron imaging can be used to follow intersystem crossing in molecules such as pyrazine, and we also show how the transfer of nuclear coherences can be followed with this technique. We discuss how time-resolved pump?probe photofragment imaging can be used to follow unimolecular decomposition of free radicals with small reaction barriers and we show how this can lead to non-statistical behaviour as a result of restricted rovibrational coupling. Finally, we describe recent applications of pump?probe Coulomb explosion imaging which has the potential to image directly the nuclear wavefunction throughout the course of a chemical reaction. The review closes with some brief conclusions and pointers for future work.