# THE FIRST ABSORPTION B AND OF $H_{2}S$: A PROBE OF RED WING FEATURES VIA PHOTOFRAGMENTATION DYNAMICS

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 Title: THE FIRST ABSORPTION B AND OF $H_{2}S$: A PROBE OF RED WING FEATURES VIA PHOTOFRAGMENTATION DYNAMICS Creators: Wasserman, T. A. W.; Arias, A. A.; Müller, Thomas; Vaccaro, P. H. Issue Date: 1995 Publisher: Ohio State University Abstract: The first absorption band of hydrogen sulfide peaks at ${\sim} 196$ nm and displays only vestiges of vibronic structure owing to lifetime broadening ascribed to a rapid predissociation process. The unrelaxed SH radicals formed subsequent to 266 nm excitation have been used to probe the extreme red edge of this electronic system. While nonradiative decay of the SH $A^{2}\Sigma^{+}$ state limits the overall utility of fluorescence-based spectroscopies, implementation of the "absorption-like" Degenerate Four-Wave Mixing (DFWM) scheme within the SH A-X transition has enabled reliable extraction of dynamical information even under conditions of low target number density $(e.g., <10^{11} molecules/quantum state/cm^{3})$. These experiments reveal a "cold" non-Boltzmann rotational distribution of nascent SH molecules $[T_{eff}(^{2}\Pi_{3/2}) \approx 320K and T_{eff}(^{2}\Pi_{1/2}) \approx 270K]$ created exclusively within the vibrationless level of their ground electronic state, with a nonstatistical population of the two spin-orbit states but no preference for individual lambda-doublet components. More importantly, our laboratory measurements show no net alignment of angular momentum in the photofragments $(A_{0}^{(2)} \approx 0)$ and give no indication of spatial or translational anisotropy $(\beta_{eff} = 0)$. Both of these results are consistent with a slow predissociation mechanism involving a long-lived intermediate complex. Although further efforts are required to clarify the origins of such findings, it appears that a critical evaluation of accepted notions regarding the spectroscopy and photochemistry of $H_{2}S$ is more than warranted. Description: Author Institution: Yale University, New Haven, CT 06511. URI: http://hdl.handle.net/1811/29776 Other Identifiers: 1995-TD-09