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

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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.