Rotational interactions in autoionizing Rydberg states of ammonia

Double-resonance ionization spectra via selected rotational levels of the C̃′ 1A′(0100) state of ammonia show direct evidence for rotational-electronic perturbations between Rydberg series converging to different rotational states of NH3+ X̃ 2A2″ (0100), and for rotational autoionization when it is energetically allowed. The simplicity of the double resonance spectra is quite striking, and rotational interactions with ΔN+=−1, ΔK+=0 are found to be most important. The results have implications for understanding intensities in rotationally resolved threshold photoelectron spectra and for extracting ionization onsets from photoionization mass spectra.