A photoelectron spectroscopic study of (3+1) resonant multiphoton ionization of NO and NH3

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Abstract
In the present work, we have measured energy spectra and angular distributions of photoelectrons emitted by three‐photon resonant four‐photon ionization of NO and NH3 in the gas phase. The following conclusions have been obtained: (1) Ionization of NO through the Rydberg F and H (H′) states at v′=0 and 1 gives rise to the ground‐state ion with v=0 and 1, respectively, by a Δv=0 transition; (2) Ionization of NH3 through the Rydberg C′ states with v′=0–5 gives rise to the ground‐state ion with v=0–5, respectively, by Δv=0 transitions; (3) Photoelectron angular distributions obtained for the (3+1) processes may well be interpreted in terms of cosine‐square distributions. This fact strongly indicates that the ionization step takes place by one‐photon direct ionization from the three‐photon resonant states.