Abstract
Emission from several electronically excited states of NS is observed when the energetic molecule S4N4 is photolyzed with radiation from an excimer laser. Photolysis at 248 nm generates fluorescence from the B 2Π1/2,3/2, H 2Π1/2, G 2Σ−, and I 2Σ+ states of NS. NS(B 2Π1/2,3/2) and NS(C 2Σ+) fluorescence is observed when the photolysis wavelength is changed to 222 nm. The NS(H) and NS(C) spectra are postulated to arise from a resonant interaction between the KrF and KrCl excimer photons, respectively, and vibrationally hot ground state NS. LIF excitation scans on the NS X 2Π1/2,3/2 → B 2Π1/2,3/2 system confirm the production of rotationally and vibrationally excited NS(X) up to v″=4. A mechanism, based on the experimental data (i.e., spectral composition, laser fluence studies, excited state time histories), calculated heats of formation, and Gaussian molecular orbital calculations, is proposed to account for the observed emissions. For photolysis at 248 nm it is hypothesized that a two photon absorption promotes the ground singlet state of S4N4 to an upper repulsive singlet state, which rapidly dissociates (τ≪30 ns), producing an acyclic S3N3 fragment and vibrationally excited monomeric NS(X). The photofragments can interact further with the excimer radiation to produce NS(B) and NS(H), respectively. A similar mechanism is proposed to account for the presence of the NS(B) and NS(C) excited states for the 222 nm photolysis.
Published Version
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