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 K_a 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 K_a 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.