Observation of dissociative and radiative states of N2H by neutralized ion beam techniques

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Abstract
The N2 H(D) radical has been studied experimentally by measurement of the kinetic energy release in its unimolecular dissociation following formation by electron transfer from metal atoms to high velocity, mass-resolved ion beams and theoretically by ab initio techniques. Calculations of the dissociation coordinate of the ground state radical at the MP4/6-311G**//MP3/6-311G** level of theory indicate that the radical is unstable with respect to N2 and H by 0.6 eV but separated from the dissociation products by a 0.4 eV barrier. One dimensional tunneling lifetimes are determined to be 7.0×10−12 s for N2 H and 3.6×10−10 s for N2 D. Neutralization of the ion by Zn targets produces predominantly radicals in the 2 A′ ground state with dissociative lifetimes τ<0.5 μs, in agreement with the calculations. Mg targets produce the radical in a mixture of the 2A′ ground and 2A″(π) excited states with a branching ratio dependent on the internal energy of the precursor ion. A higher excited state of the radical, suggested to be an n=3 Rydberg level, is produced with K targets and is inferred to undergo radiative transitions, probably containing some discrete structure, to the lower 2A′ and 2A″(π) states in the wavelength range of 2700–4500 Å. Observations of these transitions may constitute the first spectroscopic observation of the radical.