Transitions between states of high angular momentum in the electronic spectrum of NH2

Abstract

Electronic spectra of the NH2 radical have been recorded as LIF excitation spectra of the products of photolysis of NH3 in its ÖX bands; as dispersed-emission spectra following laser excitation with this same source; and as emission spectra from a discharge through ammonia recorded with a Fourier-transform spectrometer. All these spectra are dominated by transitions in which the a-axis rotation is excited to high values of the Ka quantum number. By combination of these experimental data with model calculations all the strong features in the spectra have been assigned. The ‘semi-rigid bender’ Renner–Teller hamiltonian gives an adequate representation of these spectra of all Ka provided that v2 is low, but there are strong stretch–bend interactions at higher v2. The excitation mechanism in a cold supersonic discharge source is thought to involve the initial dissociation to NH2+ H of NH3 excited via its à state by electron collision, followed by excitation of the NH2 in a second such collision.