Theoretical study of laser-cooled SH^– anion

The potential energy curves, dipole moments, and transition dipole moments for the \begin{document}${{\rm{X}}^1}{\Sigma ^ + }$\end{document}, \begin{document}${{\rm{a}}^3}\Pi $\end{document}, and \begin{document}${{\rm{A}}^1}\Pi $\end{document}electronic state of sulfur hydride anion (SH – ) are calculated by using the multi-reference configuration interaction method plus Davidson corrections (MRCI+ Q ) with all-electron basis set. The scalar relativistic corrections and core-valence correlations are also considered. In the CASSCF calculations, H(1s) and S(3s3p4s) shells are chosen as active space, and the rest orbitals S(1s2s2p) as closed-shell. In the MRCI+ Q calculations, the S(1s2s2p) shells are used for the core-valence correlation. Spectroscopic parameters, Einstein spontaneous emission coefficient, Franck-Condon factors, and spontaneous radiative lifetimes are obtained by using Le Roy’s LEVEL8.0 program. The calculated spectroscopic parameters are in good agreement with available experimental data and theoretical values. Spin-orbit coupling (SOC) effects are evaluated with Breit-Pauli operators at the MRCI+ Q level. Transition dipole moments (TDMs) for the \begin{document}${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}, \begin{document}${{\rm{a}}^3}{\Pi _{{0^ + }}} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}, \begin{document}${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}, \begin{document}${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{a}}^3}{\Pi _{{0^ + }}}$\end{document}and \begin{document}${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{a}}^3}{\Pi _1}$\end{document}transitions are also calculated. The strength for the \begin{document}${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}is the strongest in these five transitions, the value of TDM at R e is –1.3636 D. We find that the value of TDM for the \begin{document}${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}transition at R e is 0.5269 D. Therefore, this transition must be taken into account to build the scheme of laser-cooled SH – anion. Highly diagonally distributed Franck-Condon factor f 00 for the \begin{document}${{\rm{a}}^3}{\Pi _1}(\nu ' = 0) \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}\begin{document}$ (\nu '' = 0)$\end{document}transition is 0.9990 and the value for the \begin{document}${{\rm{A}}^1}{\Pi _1}(\nu ' = 0) \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + (\nu '' = 0)$\end{document}transition is 0.9999. Spontaneous radiative lifetimes of \begin{document}$\tau \left( {{{\rm{a}}^3}{\Pi _1}} \right)= 1.472 \;{\text{μ}}{\rm{s}}$\end{document}and \begin{document}$\tau \left( {{{\rm{A}}^1}{\Pi _1}} \right)=0.188 \;{\text{μ}}{\rm{s}}$\end{document}are obtained, which can ensure that laser cools SH – anion rapidly. To drive the \begin{document}${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}and \begin{document}${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}transitions, just one laser wavelength is required. The wavelengths are 492.27 nm and 478.57 nm for two transitions, respectively. Notably, the influences of the intervening states \begin{document}${{\rm{a}}^3}{\Pi _1}$\end{document}and \begin{document}${{\rm{a}}^3}{\Pi _{{0^{\rm{ + $\end{document}on the \begin{document}${{\rm{A}}^1}{\Pi _1} \leftrightarrow {X^1}\Sigma _{{0^ + }}^ + $\end{document}transition are small enough to implement a laser cooling project. A spin-forbidden transition and a three-electronic-level transition optical scheme of laser-cooled SH – anion are constructed, respectively. In addition, the Doppler temperatures and recoil temperatures for the \begin{document}${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}and \begin{document}${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $\end{document}transitions of laser-cooled SH – anion are also obtained, respectively.