# SEP-DFWM STUDIES OF JET-COOLED $S_{2}O$: EXPLORATION OF THE GROUND STATE POTENTIAL ENERGY HYPERSURFACE NEAR 1 EV OF VIBRATIONAL ENERGY

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 Title: SEP-DFWM STUDIES OF JET-COOLED $S_{2}O$: EXPLORATION OF THE GROUND STATE POTENTIAL ENERGY HYPERSURFACE NEAR 1 EV OF VIBRATIONAL ENERGY Creators: Dupré, Patrick; Zhang, Q.; Müller, Thomas; Vaccaro, P. H. Issue Date: 1995 Abstract: The $\tilde{X}_{1} A^{\prime}$ ground electronic potential surface of the transient disulfur monoxide $(S_{2}O)$ molecule has been examined in regions corresponding to roughly 1 eV of vibrational excitation. $S_{2}O$ molecules were prepared in situ under cold $(T_{rot} = 1K)$ supersonic free-jet expansion conditions and interrogated via a nonlinear variant of Stimulated Emission Pumping (SEP) based upon Degenerate Four-Wave Mixing (DFWM) spectroscopy. while the background-free, "absorption-like" response of the sub-Doppler SEP-DFWM technique offers unique advantages over more conventional fluorescence-dip methods, the quadratic dependence of DFWM signal amplitude upon number density would seem to limit this approach to the study of stable molecules maintained in high-pressure, static bulb environments. Nevertheless, by utilizing the intense $S_{2}O \tilde{C}^{1}A^{\prime} - \tilde{X}^{1}A^{\prime} (\pi^{\ast} \leftarrow \pi)$ transition at ${\sim}30900 cm^{-1}$ as the first step in an optical-optical double resonance scheme, ongoing SEP-DFWM experiments have demonstrated excellent signal-to-noise ratios for target species entrained in seeded molecular beams. The substantial elongation of the S-S bond upon $\tilde{C} \leftarrow \tilde{X}$ electron promotion provides Franck-Condon access to ground state levels of $S_{2}O$ having substantial amplitude in the $\nu_{2} S-S$ stretching mode. Analysis of vibronic features observed subsequent to $2^{2}_{0}$ and $2^{3}_{0}$ excitation yields values of $\omega_{2} = 680 cm^{-1}$ and $x_{22} = -2.4 cm^{-1}$ for the frequency and anharmonicity of $\nu_{2}$ in $\tilde{X}^{1}A^{\prime} S_{2}O$. These results will be discussed in conjunction with various experimental configurations for SEP detection by means of resonant four - wave mixing. URI: http://hdl.handle.net/1811/29664 Other Identifiers: 1995-RH-08