Theoretical study of spectroscopic properties of 5 -S and 10 states and laser cooling for AlH+ cation

In this paper, we calculate the potential energy curves of 5 -S and 10 , which arise from the first two dissociation limits of the AlH+ cation. The calculations are done using the complete active space self-consistent field method, which combines with the valence internally contracted multireference configuration interaction plus the Davidson modification (icMRCI+Q) approach with the aug-cc-pV6Z basis set. To improve the reliability and accuracy of the potential energy curves, the core-valence correlation and scalar relativistic correction, as well as the extrapolation of potential energy to the complete basis set limit are taken into account. The spin-orbit coupling is computed using the state interaction approach with the Breit-Pauli Hamiltonian. Employing the potential energy curves obtained in this study, we evaluate the spectroscopic parameters and vibrational levels for the bound and quasi-bound 4 -S and 8 states. The computed spectroscopic constants of X2+ and A2 states are all in agreement with the available experimental data. Moreover, the present theoretical energy separations between each higher channel (Al+(3P0) + H(2S1/2), Al+(3P1) + H(2S1/2), and Al+(3P2) + H(2S1/2) and the lowest one (Al+(1S0) + H(2S1/2)) are in excellent agreement with the experimental values. The transition dipole moments are calculated using the valence internally contracted multireference configuration interaction approach with the aug-cc-pV6Z basis set for the 2(1/2) X21/2+ and A23/2X21/2+. Based on the obtained potential energy curves and transition dipole moments, highly diagonally distributed Franck-Condon factors (f00 and f11) and large vibrational branching ratios are determined for the 2(1/2)1st well (v'=0, 1) X21/2+ (v) and A23/2(v'=0,1)X21/2+(v) transitions; short spontaneous radiative lifetime and narrow radiative width for the 2(1/2)1st well (v'=0, 1) and A23/2 (v'=0, 1) are also predicted in this study, which are suitable for the rapid laser cooling of the AlH+ cation. The three required laser cooling wavelengths are all in the ultraviolet region, that is, 1) for the X21/2+(v) 2(1/2)1st well (v') transition:the main repumping laser 00=358.74 nm, two repumping lasers 10=379.27 nm and 21=374.86 nm; 2) for the X21/2+ (v) A23/2 (v') transition:the main repumping laser 00=357.43 nm, two repumping lasers 10=377.80 nm and 21=373.26 nm. In addition, the recoil temperature for the X21/2+ (v=0) 2(1/2)1st well (v'=0) and X21/2+ (v=0) A23/2 (v'=0) transitions are obtained. The results imply the feasibility of laser cooling of AlH+ cation. In addition, the spin-orbit coupling effect on the spectroscopic parameter, vibrational level, and laser cooling of AlH+ cation are evaluated.