Nuclear and electron dynamics from femto- and subfemto-second time-resolved photoelectron angular distributions

We explore the application of a quantum vibrational wavepacket dynamics formulation of femtosecond energy- and angle-resolved photoelectron spectroscopy to the study of nuclear and electron dynamics. The formulation incorporates geometry- and energy-dependent photoionization matrix elements and is well suited for studies of nonadiabatic dynamics where nuclear and electronic degrees of freedom are coupled. In this paper we explore two aspects of angle-resolved pump-probe photoelectron spectroscopy, using NO2 and NaI as examples. The first is a refinement of femtosecond photoelectron spectroscopy in which the time derivative of the velocity map image is seen to more readily characterize the nuclear wavepacket dynamics in non-adiabatic regions. The other is an analysis to extract the effects of electronic-state fluctuation from sub-femtosecond scale photoelectron dynamics. Within the framework of the Born-Huang (Oppenheimer) expansion where the total wavefunction is expressed in products of stationary-state electronic wavefunctions and time-dependent nuclear wavepackets, we seek to identify how the effect of electron dynamics might be manifested in principle.