Photoionization dynamics of the NO A 2Σ+ state deduced from energy- and angle-resolved photoelectron spectroscopy

The direct photoionization process NO A 2Σ+ (v=0, N=13)→NO+ X 1Σ+ (v+=0, N+)+e− is studied by energy- and angle-resolved photoelectron spectroscopy by employing two-color resonance-enhanced multiphoton ionization (REMPI) via excitation of the NO A–X(0–0) R21(11.5) transition. The photoelectron angular distributions (PADs) associated with individual rotational levels N+ of the ion are determined. Combined analysis of the newly obtained PADs and those reported earlier for the processes NO A 2Σ+ (v=0, N≥20)→NO+ X 1Σ+ (v+=0, N+)+e− via P21+Q1 branch excitation shows that the photoionization dynamics is independent of the rotational quantum number of state to be ionized and of the spin state of the photoelectron. Quantitative comparison of our results with threshold photoelectron measurements provides strong evidence that ionization in the pulsed-electric-field threshold technique is not via direct photoionization.