Dissociation lifetimes and level mixing in overtone-excited HN3(X̃ 1A′)

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Abstract
Vibrational overtone photodissociation is used to examine the spectroscopy and vibrational predissociation lifetimes of HN3 in its ground electronic state. Direct overtone pumping of the N–H stretching levels 5νNH and 6νNH prepares molecules in selected states (v,J,K) near 15 100 and 17 700 cm−1 of vibrational energy; spin‐forbidden NH(X 3 Σ−) dissociation fragments are detected by laser‐induced fluorescence. Photodissociation spectra of beam‐cooled HN3 display mixing of individual rotational levels of the nνNH vibrations with several background states, with derived coupling matrix elements in the range 0.01–0.1 cm−1. Vibrational predissociation lifetimes of mixed components of 5νNH are state specific, with variations of a factor of 2 for only 0.1 cm−1 energy differences. Average lifetimes for low J, K are 210 ns for 5νNH and 0.95 ns for 6νNH. The ratio of decay rates for the two overtone levels, k(6νNH)/k(5νNH)=220, is much greater than predicted by statistical theory, which gives a ratio of 4.