Theoretical study of spin-forbidden cooling transitions of indium hydride using ab initio methods

The feasibility of spin-forbidden cooling of the InH molecule is investigated based on ab initio quantum chemistry calculations. The potential energy curves for the X¹Σ₀₊⁺, a³Π_0-, a³Π₀₊, a³Π₁, a³Π₂, A¹Π₁, 1³Σ_0-⁺, and 1³Σ₁⁺ states of InH are obtained based on multi-reference configuration interaction plus the Davidson corrections method. The calculated spectroscopic constants are in good agreement with the available experimental data. In addition, the influences of the active space and spin-orbit coupling effects on the potential energy curves and spectroscopic constants are also studied. For R_e of a³Π_0-, a³Π₀₊, a³Π₁, and a³Π₂ states, the error from large active space is small. The potential energy curve of the A¹Π₁ state is not smooth for small active space. The spin-orbit coupling effects have great influences on the potential well depth and equilibrium internuclear distance of the A¹Π state. The Franck-Condon factors and radiative lifetimes are obtained on the basis of the transition dipole moments of the a³Π₀₊→X¹Σ₀₊⁺,a³Π₁→X¹Σ₀₊⁺,and A¹Π₁→X¹Σ₀₊⁺ transitions. Our calculation indicates that the a³Π₁(v'=0)→X¹Σ₀₊⁺(v=0) transition provides a highly diagonally distributed Franck– Condon factor and a short radiative lifetime for the a³Π₁ state, which can ensure rapid and efficient laser cooling of InH. The proposed laser drives a³Π₀₊→X¹Σ₀₊⁺ transitions by using three wavelengths.