Theoretical laser cooling feasibility study of ZrH molecule at the fine structure level.

A theoretical electronic structure calculation of the ZrH molecule is conducted via <i>ab initio</i> Complete Active Space Self-Consistent Field and the Multireference Configuration Interaction with Davidson correction calculation (CASSCF/MRCI + Q). The adiabatic potential energy curves (PECs) for the 53 low-lying electronic states in the representations of ^2s+1Λ^(+/-) and Ω^(+/-) for ZrH molecule have been investigated along with the internuclear distance R_e, the harmonic frequency ω_e, the dipole moment μ, the rotational constant B_e and the electronic transition energy with respect to the ground state T_e. are calculated. By using the canonical function approach, the vibrational energy E_v, the rotational constants B_v, the centrifugal constants D_v, and the turning points R_min and R_max have been calculated up to the vibrational level v = 18. Based on the investigated data, the Franck-Condon factors, the Einstein coefficient, the radiative lifetimes, and the vibrational branching ratio for the transitions X²Δ_3/2 - (1)⁴Φ_3/2, X²Δ_3/2 - (1)⁴Φ_5/2, X²Δ_3/2 - (1)²Π_3/2 have been calculated. The large value of the radiative lifetimes in (ms) for these transitions proves that this molecule is not a good candidate for direct laser cooling.