HIGH RESOLUTION SPECTROSCOPY AND PHOTOPHYSICS OF TRANSITION METAL CONTAINING DIATOMIC MOLECULES: THE $C^{4}\Sigma^{-}-X^{4}\Sigma^{-}$ SYSTEM OF NIOBIUM SULPHIDE

Author Institution: Laser Chemistry Group, Division of Chemistry, National Research Council of CanadaThe $C^{4}\Sigma^{-}-X^{4}\Sigma^{-}$ system of niobium sulphide, NbS, has been studied in a molecular beam apparatus by laser-induced fluorescence. A vibronic analysis has been carried out and leads to the following constants: $-544.0 cm^{-1}, \omega_{\ast}x^{**}_{\ast}-1.7 cm^{-1}, \omega'_{\ast} -489.6 cm^{-1}, \omega_{\ast}x'_{\ast} -2.7 cm^{-1}$. The data clearly show that the coupling scheme in both the C and X states are best described as case (a). A weak satellite band lying $62.7 cm^{-1}$ from the R-head of the $c^{4}\Sigma_{3/2}^{-}-x^4\Sigma^4 \Sigma_{3/2}^{-1}$ sub-band could not be fitted to the C-X system. This band is tentatively assigned as a $^{2}\Sigma^{*}-x^{4}\Sigma^{-}_{1/2}$ transition where the $^{2}\Sigma^{\ast}$ state contains a large admixture of $C^{\ast}\Sigma^{-}_{1/2}$ character. The dispersed emission spectrum resulting from the decay of the $^{2}\Sigma^{\ast}$ state leads to an energy separation of about $62 cm^{-1}$ between the $X^{4}\Sigma^{-}_{1/2}$ and the $X^{4}\Sigma^{-}_{3/2}$ components. The energy separation between the $C^{4}\Sigma^{-}_{1/2}$ and the $C^{4}\Sigma^{-}_{3/2}$ components is highly dependent of the vibrational energy content and is about 80, 77, 73, 63 and $62 cm^{-1}$ for the vibrational levels 0, 1, 2, 3 and 4 respectively. The (0,0) band has also been investigated at high resolution and this allowed the nuclear magnetic hyperfine structure, which arises from the interaction of a metal centered unpaired electron with the magnetic nucleus of niobium (I-9/2) to be resolved. A preliainary analysis will be presented