Photoelectron spectroscopy of autoionizing Rydberg states of ammonia

Photoelectron spectroscopy was used to determine the ionic vibrational dist ributions following vibrational autoionization of Rydberg states of NH3. Tw o-color, two-photon resonant, three-photon excitation via selected rotation al levels of the NH3 (C) over tilde' (1)A(1)'(0200) intermediate state was employed to populate vibrationally autoionizing Rydberg states between the v(2)(+)=1 and v(2)(+)=2 ionization thresholds of the NH3+ (X) over tilde (2 )A(2)" ground electronic state. As expected from the propensity rule for vi brational autoionization, ionization with Delta v(2)=-1 was found to be the dominant process. The observed vibrational distributions appear to be inde pendent of the rotational quantum number of the autoionizing state. Partial ly resolved rotational structure was exhibited within the photoelectron spe ctra providing information on the assignments of the Rydberg states and on the mechanism for vibrational autoionization. (C) 2000 American Institute o f Physics. [S00219606(00)00109-4].