NEW SINGLET RYDBERG STATES OF THE NH(ND) RADICAL IN THE ENERGY-RANGE 92000-100000 CM-1 CHARACTERIZED BY RESONANCE ENHANCED MULTIPHOTON IONIZATION-PHOTOELECTRON SPECTROSCOPY

Two new singlet excited electronic states of the imidogen radical have been characterized through (i) analysis of the two photon resonance enhancements they provide in the wavelength resolved multiphoton ionization spectrum of a (1)DELTA state NH (ND) radicals and (ii) measurements of the kinetic energy of the photoelectrons accompanying the multiphoton ionization process. The i (1)PI state is shown to involve a ...3-sigma(2)1-pi(1) ion core and a Rydberg electron of mixed 3p-sigma/3d-sigma character. The zero-point level of this state in ND exhibits an anomalously large LAMBDA-doubling. Photoelectron kinetic energy release measurements reveal that 2 + 1 resonance enhanced multiphoton ionization via the j (1)DELTA state of NH leads to population of a range of upsilon+ vibrational levels in the ground state ion and, importantly, to a substantial population of electronically excited B (2)DELTA state ions. We conclude that the j (1)DELTA state of NH (ND) also involves a mixture of configurations, including ...3-sigma(2)1-pi(1)3d-pi(1) and the core excited configuration ...3-sigma(1)1-pi(2)3s-sigma(1). All observed vibrational levels of this state in both NH and ND show perturbations, some of which have proved amenable to analysis.