Angle- and energy-resolved photoelectron spectroscopy: A probe of photoionization dynamics

The dynamics of photoionization are explored through a two-color high-resolution angle- and energy-resolved study of the photoelectrons produced in the (1 + 1{dollar}spprime{dollar}) resonance enhanced multiphoton ionization of NO via the {dollar}Asp2Sigmasp+{dollar} ({dollar}nu{dollar} = 0) state. We find markedly different photo-electron angular distributions arising from production of ions in different rotational states ({dollar}Delta{dollar}N = 0, {dollar}pm{dollar}1, {dollar}pm{dollar}2 transitions in the ionization step). We also observe that the {dollar}Delta{dollar}N = {dollar}pm{dollar}2 angular distributions are very sensitive to the intermediate state alignment. A general model is put forward in which experimental observables (angle- and energy-resolved photoelectron spectra) are used to determine the attributes (relative amplitudes and phase shifts) of a small number of interfering continuum channels that contribute to the ionization step as well as the fraction of parallel character of the ionization step. Nearly 70% of the ejected photoelectrons are associated with the {dollar}Delta{dollar}N = 0 ionization transition; the partial wave composition of these electrons is dominated by p-character. The less important {dollar}Delta{dollar}N = {dollar}pm{dollar}1 peaks have both s- and d-wave character. The {dollar}Delta{dollar}N = {dollar}pm{dollar}2 photoelectron peaks exhibit far more f-wave than p-wave character because destructive interference removes nearly all of the p-wave contribution to the angular distribution. The partial wave decomposition is used to predict angular distributions resulting from excitation of the intermediate state by different rotational branch transitions; these predictions are in excellent agreement with the measured distributions.