The potential energy curves, dipole moments, and transition dipole moments for the
${{\rm{X}}^1}{\Sigma ^ + }$
,
${{\rm{a}}^3}\Pi $
, and
${{\rm{A}}^1}\Pi $
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+
Qcalculations, 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+
Qlevel. Transition dipole moments (TDMs) for the
${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
,
${{\rm{a}}^3}{\Pi _{{0^ + }}} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
,
${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
,
${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{a}}^3}{\Pi _{{0^ + }}}$
and
${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{a}}^3}{\Pi _1}$
transitions are also calculated. The strength for the
${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
is the strongest in these five transitions, the value of TDM at
R
eis –1.3636 D. We find that the value of TDM for the
${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
transition at
R
eis 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
00for the
${{\rm{a}}^3}{\Pi _1}(\nu ' = 0) \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
$ (\nu '' = 0)$
transition is 0.9990 and the value for the
${{\rm{A}}^1}{\Pi _1}(\nu ' = 0) \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + (\nu '' = 0)$
transition is 0.9999. Spontaneous radiative lifetimes of
$\tau \left( {{{\rm{a}}^3}{\Pi _1}} \right)= 1.472 \;{\text{μ}}{\rm{s}}$
and
$\tau \left( {{{\rm{A}}^1}{\Pi _1}} \right)=0.188 \;{\text{μ}}{\rm{s}}$
are obtained, which can ensure that laser cools SH
–anion rapidly. To drive the
${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
and
${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
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
${{\rm{a}}^3}{\Pi _1}$
and
${{\rm{a}}^3}{\Pi _{{0^{\rm{ + }}}}}$
on the
${{\rm{A}}^1}{\Pi _1} \leftrightarrow {X^1}\Sigma _{{0^ + }}^ + $
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
${{\rm{a}}^3}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
and
${{\rm{A}}^1}{\Pi _1} \leftrightarrow {{\rm{X}}^1}\Sigma _{{0^ + }}^ + $
transitions of laser-cooled SH
–anion are also obtained, respectively.
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