Knowledge Bank

The $C4\Sigma --X4\Sigma -$ 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: $-544.0cm-1,\omega \ast x\ast \ast \ast -1.7cm-1,\omega \ast \prime -489.6cm-1,\omega \ast x\ast \prime -2.7cm-1$. 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 $62.7cm-1$ from the R-head of the $c4\Sigma 3/2--x4\Sigma 4\Sigma 3/2-1$ sub-band could not be fitted to the C-X system. This band is tentatively assigned as a $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma \ast -x4\Sigma 1/2-$ transition where the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma \ast$ state contains a large admixture of $C\ast \Sigma 1/2-$ character. The dispersed emission spectrum resulting from the decay of the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma \ast$ state leads to an energy separation of about $62cm-1$ between the $X4\Sigma 1/2-$ and the $X4\Sigma 3/2-$ components. The energy separation between the $C4\Sigma 1/2-$ and the $C4\Sigma 3/2-$ components is highly dependent of the vibrational energy content and is about 80, 77, 73, 63 and $62cm-1$ 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.