Wavepacket Dynamics via Femtosecond Time-resolved Photoelectron and Photoionization Spectroscopy

Abstract

An emerging goal of fs pump-probe spectroscopy is the study of chemical reaction dynamics of polyatomic molecules and it is important to develop methods for their study. We describe such an experiment by S(t) = |<f|μ(Q)|ex(t)>|2 where S(t) is the measurement, |f> is the final state, used as a 'template' onto which we project the dynamics, μ(Q) is the coordinate dependent dipole coupling, and |ex(t)> is the wavepacket that we wish to study. In general, the choice of the final state |f> must take into consideration several effects: (1) In order to decompose the evolving wavepacket in the basis of the final states, |f> must be well known (unfortunately, higher excited states of polyatomic molecules are poorly known); (2) Variation of the dipole coupling between electronic states during the wavepacket evolution (i.e. due to non-adiabatic effects) will have a strong effect on the measured signals. It is important to choose a technique which 'follows' the reaction dynamics, even to 'dark' states. (3) Polyatomic reaction dynamics implies multidimensional wavepackets with many frequency components.