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

The N₂H(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 N₂H and 3.6 × 10^-10 s for N₂D. Neutralization of the ion by Zn targets produces predominantly radicals in the ²A′ 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.