STIMULATED EMISSION SPECTROSCOPY OF ACETYLENE. STRUCTURE OF THE $\tilde{X}^{1}\Sigma_{g}^{+}$ STATE AT $28000 cm^{-1}$
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Date
1983
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Ohio State University
Abstract
The $28000 cm^{-}1$ region of the $\tilde{X}^{1}\Sigma_{g}^{+}$ state af HCCH is examined by Stimulated Emission Pumping (SEP) from the $v_{3} = 2$ and $3,K = 1$ levels of the trans-bent $\tilde{A}^{1} A_{u}$ excited state. In contrast to the situation for high overtone spectroscopy which accesses primarily C-H overtones of u-symmetry. SEP samples C-C and trans-bend levels of g-symmetry. Among the most striking features in the SEP spectra are - $2 cm^{-1}$ wide dumps (about 1 clump per $10 cm^{-1}$) each consisting of - 20 $0.02 cm^{-1}$ wide lines. The clumps appear to be $K^{\prime} = 1 \rightarrow K^{\prime\prime} = 0$ sub-bands. Although no correlation has been found between the fine structure of clumps observed for consecutive $J^{\prime\prime}$ values., the centers of gravity for all observed clumps appear to be well described by a rotational constant B = $1.166 cm^{-1}$ which is surprisingly similar to the value B = $1.177 cm^{-1}$ for the vibrationless level. Density of state calculations suggest that each clump corresponds to a combination of the three totally symmetric normal modes (in $C_{2_{h}}$ these are C-C stretch, symmetric H-C stretch, and trans-bend) and that the lines within each clump correspond to all states of $A_{g}({\Sigma_{g}}^{+})$ symmetry.
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Author Institution: Department of Chemistry, Massachusetts Institute of Technology