# SEP Spectroscopy of the $\tilde{B}^{2}A'-\tilde{X}^{2}A'$ System of Jet-cooled HCO and DCO: Vibrational Structure of the $\tilde{X}^{2}A'$ State Near and Above Dissociation

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 Title: SEP Spectroscopy of the $\tilde{B}^{2}A'-\tilde{X}^{2}A'$ System of Jet-cooled HCO and DCO: Vibrational Structure of the $\tilde{X}^{2}A'$ State Near and Above Dissociation Creators: Dunlop, James R.; Tobiason, J. D.; Rohlfing, Eric A. Issue Date: 1994 Publisher: Ohio State University Abstract: The formyl radical, HCO, is an important combustion intermediate that has been studied by a variety of spectroscopic techniques. Despite this, the ground-state potential energy surface and vibrational structure near the dissociation barrier are not fully understood. We use stimulated emission pumping (SEP), via either two-color resonant four-wave mixing (RFWM) or fluorescence depletion, to observe a wide range of vibrational levels in the $\widetilde{X}_{2}A^{\prime}$ state of HCO and DCO. The combination of the two techniques provides determinations of energies and widths of vibrational states above and below the threshold for dissociation into H+CO. Spectra of $\widetilde{X}_{2}A^{\prime}$ state C-O stretch, bend and combination levels obtained by pumping the $\widetilde{B}^{2}A^{\prime} - \widetilde{X}^{2}A^{\prime}$ electronic origin confirm the applicability of RFWM-SEP and yield new results. Spectra involving the C-H stretch in the $\widetilde{X}^{2}A^{\prime}$ state, obtained by pumping one quanta of C-H stretch in the $\widetilde{B}^{2}A^{\prime}$ state, provide new experimental data showing the enhancement in dissociation rate upon C-H excitation. The C-H stretch and bending levels show interesting mode specific dissociation rates that are compared to recent theoretical calculations. In contrast to HCO, only a small spectroscopic data set exisits for DCO. Results for DCO are among the first experimental data to probe its ground-state vibrational structure. Both sets of results will be helpful in a more rigorous determination of the potential energy surface for the $\widetilde{X}^{2}A^{\prime}$ state. Description: This work was supported by the U.S. Department of Energy, Office of Basis Energy Sciences, Chemical Sciences Division. Author Institution: Sandia National Laboratorics, Combustion Research Facility URI: http://hdl.handle.net/1811/13104 Other Identifiers: 1994-RA'-02