THE ELECTRONIC SPECTRUM OF $CoCl_{2}$ IN THE GAS PHASE

$^{a}$ S. H. Ashworth, F. J. Frieman, and J. M. Brown, J. Chem. Phys., 104, 48, (1996). $^{b}$ C. W. DeKock and D. M. Gruen, J. Chem. Phys., 44, 4387, (1966). $^{c}$ V. V. Sliznev, N. Vogt, and J. Vogt, The Eighteenth Colloquium on High Resolution Molecular Spectroscopy, Dijon, Poster O4, (2003). $^{d}$ F. J. Grieman, S. H. Ashworth, and J. M. Brown, J. Chem. Phys., 92, 6365, (1990).Author Institution: Physical and Theoretical Chemistry Laboratory; Chemistry Department, Macalester CollegeThe 310 nm uv band system of the $CoCl_{2}$ radical has been recorded at high resolution by laser excitation spectroscopy. (The experimental details are described in full $elsewhere^{a}$). The molecule was formed in the high temperature reaction between HCl(g) and cobalt metal and was cooled to a rotational temperature of about 10K in a subsequent free-jet expansion. This work confirms earlier observations by DeKock and $Gruen^{b}$ and provides much more structural information. Excited state vibrational progressions of approximately $200 cm^{-1}$ have been identified and tentatively assigned to the symmetric stretching vibration. Rotational analyses of the three longest wavelength bands reveal that the lower and upper electronic states both have $\Omega = 7/2$; this is consistent with recent ab initio calculations which predict a $^{4}\Delta$ ground $state^{c}$. The following rotational constants were determined for the (200) band: $B^{\prime\prime} = 0.056432(81) cm^{-1}, B^{\prime} = 0.04951(10) cm^{-1}$. A study by dispersed fluorescence shows progressions in the ground state symmetric stretching vibration $(360 cm^{-1})$. This is very similar to the value determined for other transition metal $dichlorides^{d}$. Note that the suggested value for $\nu_{1}$ in the excited state is much smaller than this