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

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.