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 e nhancements they provide in the wavelength resolved multiphoton ioniza tion spectrum of a (1)DELTA state NH (ND) radicals and (ii) measuremen ts of the kinetic energy of the photoelectrons accompanying the multip hoton 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 releas e measurements reveal that 2 + 1 resonance enhanced multiphoton ioniza tion 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) an d 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 pertu rbations, some of which have proved amenable to analysis.