Laser cooling of the OH molecular anion in a theoretical investigation.

The schemes for laser cooling of the OH anion are proposed using an ab initio method. Scalar relativistic corrections are considered using the Douglas-Kroll Hamilton. Spin-orbit coupling (SOC) effects are taken into account at the MRCI+Q level. SOC effects play important roles in the transition properties of the OH anion. Transition strengths for the transition of the OH anion cannot be ignored. Large vibrational branching ratios for the and transitions are determined. Short spontaneous radiative lifetimes for the aΠ and AΠ states are also predicted for rapid laser cooling. The vibrational branching loss ratio to the intervening states aΠ and aΠ for the transition is small enough to enable the building of a laser cooling project. The three required laser wavelengths for the and transitions are all in the visible region. The results imply the probability of laser cooling of the OH anion via both a spin-forbidden transition and a three-electronic-level transition.