Vibrational spectroscopy and photochemistry of hydrazoic acid

[摘要] Single photon vibrational absorption spectra of hydrazoic acid (HN$sb3$, hydrogen azide), a model unimolecular reactant, have been recorded in the 500-22500 cm$sp{-1}$ spectral region. Vibrational spectra of nitrous oxide (N$sb2$O), an isoelectronic analogue of HN$sb3$, have also been recorded in the 500-15200 cm$sp{-1}$ spectral region. At high vibrational energy (above thresholds of approximately 12600 and 18500 cm$sp{-1}$), HN$sb3$ exhibits vibrational and/or electronic predissociation to form two sets of products (N$sb2$ + NH(X$sp3Sigma$), NH*(a$sp1Delta$)) that evolve from the reactant on multiple potential energy surfaces. Spectral line broadening measurements on highly vibrationally excited states of hydrazoic acid have been performed to determine intramolecular lifetimes for vibrational predissociation and other intramolecular rate processes. Thousands of rovibronic transitions have been analyzed to yield accurate spectroscopic (rotational, vibrational) constants of NH stretch vibrational overtone states (up to 7$usb{m NH}$) and of combination states involving NH stretch overtone excitations plus one or more quanta of other vibrational modes. Absolute and/or relative absorption intensities have been measured for many vibrational bands. Extensive high resolution linewidth measurements on individual rovibronic transitions as well as spectral simulations of the linewidths of strongly overlapping transitions have been completed in order to determine lifetime broadening rates and mechanisms as a function of rovibronic excitation energy and state both below and above characteristic predissociation thresholds. Initial single photon vibrational photochemistry experiments on HN$sb3$ have also been completed. Single photon vibrational excitation of HN$sb3$ overtone (5$usb{m NH}$ and 6$usb{m NH}$) and combination band states was performed using intracavity dye laser absorption techniques. Sensitive detection of HCN and NH$sb3$ secondary products (generated by reaction of NH primary photochemical products with ethylene) was performed using intracavity photoacoustic spectroscopy techniques. Possible mode dependent reactions were explored. All of the data reported have been used to consider the nature and dynamics of highly vibrationally excited hydrazoic acid in bound as well as in predissociative regions of HN$sb3$ potential energy surfaces.

[发布机构] Rice University