Steady and Time-Resolved Photoelectron Spectra Based on Nuclear Ensembles

Semiclassical methods to simulate both steady and time-resolved photoelectron spectra are presented. These approaches provide spectra with absolute band shapes and vibrational broadening beyond the Condon approximation, using an ensemble of nuclear configurations built either via distribution samplings or nonadiabatic dynamics simulations. Two models to account for the electron kinetic energy modulation due to vibrational overlaps between initial and final states are discussed. As illustrative examples, the steady photoelectron spectra of imidazole and adenine and the time- and kinetic-energy-resolved photoelectron spectrum of imidazole were simulated within the frame of time-dependent density functional theory. While for steady spectra only electrons ejected with maximum allowed kinetic energy need to be considered, it is shown that to properly describe time-resolved spectra, electrons ejected with low kinetic energies must be considered in the simulations as well. The results also show that simulations based either on full computation of photoelectron cross section or on simple Dyson orbital norms provide results of similar quality.