New singlet Rydberg states of the NH(ND) radical in the energy range 92 000–100 000 cm−1 characterized by resonance enhanced multiphoton ionization-photoelectron spectroscopy

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Abstract
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 1Δ state NH(ND) radicals and (ii) measurements of the kinetic energy of the photoelectrons accompanying the multiphoton ionization process. The i 1Π state is shown to involve a ...3σ21π1 ion core and a Rydberg electron of mixed 3pσ/3dσ character. The zero‐point level of this state in ND exhibits an anomalously large Λ‐doubling. Photoelectron kinetic energy release measurements reveal that 2+1 resonance enhanced multiphoton ionization via the j 1Δ state of NH leads to population of a range of v+ vibrational levels in the ground state ion and, importantly, to a substantial population of electronically excited B 2Δ state ions. We conclude that the j 1Δ state of NH(ND) also involves a mixture of configurations, including ...3σ21π13dπ1 and the core excited configuration ...3σ11π23sσ1. All observed vibrational levels of this state in both NH and ND show perturbations, some of which have proved amenable to analysis.