High-resolution angle- and energy-resolved photoelectron spectroscopy of NO: Partial wave decomposition of the ionization continuum

Abstract

We report a two-color high-resolution energy- and angle-resolved study of the photoelectrons produced in the (1+1′) REMPI of NO via rotational levels of the A 2Σ+ v=0 state. We find markedly different photoelectron angular distributions arising from production of ions in different rotational states (ΔN=0,±1,±2 transitions in the ionization step). We also observe that the ΔN=±2 angular distributions are very sensitive to the intermediate state alignment. A 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 ΔN=0 ionization transition; the partial wave composition of these electrons is dominated by p character. The less important ΔN=±1 peaks have both s- and d-wave character. The ΔN=±2 photoelectron peaks exhibit far more f-wave than p-wave character because destructive interference nearly removes 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.