Theoretical investigation of laser cooling for BN- anion by ab inito calculation.

A theoretical investigation for the feasibility of laser cooling BN-anion is presented. An ab initio calculation on the three low-lying states Χ2Σ+, Α2Π and Β2Σ+ are performed at the CASSCF/MRCI + Q level. The calculated spectroscopic constants are in good agreement with the available theoretical and experimental data. Radiative properties including Franck-Condon factor, Einstein coefficients and radiative lifetimes are determined. The calculation shows that the transition B2Σ+(v')↔X2Σ+(v'') has highly diagonal FCFs, especially f00 = 0.9898, and enough short radiative lifetimes. A cooling scheme by three laser beams is proposed, which requires one main pumping laser(λ00 = 474.67 nm) and two repumping lasers (λ01 = 514.64 nm, λ12= 514.90 nm). The population dynamics of cooling is investigated with the rate equation approach. The simulation demonstrates that the population does not remain trapped within the intermediate Α2Π state. The resultant scattered photons are about2.5×104, which is expected to stop BN-anion molecule in a cryogenic beam theoretically.