A theoretical study of the excited states of CrH: Potential energies, transition moments, and lifetimes

Ab initio calculations of low-lying electronic states of CrH are presented, including potential energies, dipole and transition dipole moment (TDM) functions, and radiative lifetimes, for the X 6Σ+, A 6Σ+, 3 6Σ+ , 1 6Π, 2 6Π, 3 6Π and 6Δ. Calculation of dynamic correlation effects was performed using the multistate complete active space second order perturbation (MS-CASPT2) method, based on state-averaged complete active space SCF (CASSCF) reference wave functions obtained with seven active electrons in an active space of 16 molecular orbitals. A relativistic atomic natural orbital-type basis set from the MOLCAS library was used for Cr. Good agreement is found between the current calculations and experiment for the lowest two 6Σ+ states, the only states for which spectroscopic data are available. Potential curves for the 3 6Σ+ and 2 6Π states are complicated by avoided crossings with higher states of same symmetry, thus resulting in double-well structures for these two states. The measured band head T0 = 27,181 cm-1, previously assigned to a 6Π < 6Σ+ transition, is close to our value of T0 = 28,434 cm-1 for the 2 6Π state. We tentatively assign the ultraviolet band found experimentally at 30,386 cm-1 to the 3 6Π < 6Σ+ transition for which the computed value is 29,660 cm-1. The A 6Σ+ < 6Σ+ TDM and A 6Σ+ lifetimes are found to be in reasonable agreement with previous calculations.