Towards accurate prediction for laser-coolable molecules: relativistic coupled-cluster calculations for yttrium monoxide and prospects for improving its laser cooling efficiencies

Abstract

Benchmark relativistic coupled-cluster calculations for yttrium monoxide (YO) with accurate treatment of relativistic and electron correlation effects are reported. The spin–orbit mixing of ²Π and ²Δ is found to be an order of magnitude smaller than previously reported in the literature. Together with the measurement of the lifetime of the A′²Δ_3/2 state, it implies an enhanced capability of a narrow-line cooling scheme to bring YO to sub-recoil temperature. The computed electronic transition properties also support a four-photon scheme to close the leakage of the A²Π_1/2 ↔ X²Σ_1/2⁺ cycle through the A′²Δ_3/2 state by repumping the A′²Δ_3/2 state to the B²Σ_1/2⁺ state, which subsequently decays back to X²Σ_1/2⁺. Relativistic coupled-cluster methods, capable of providing accurate spectroscopic parameters that characterize the local potential curves and hence of providing accurate Franck–Condon factors, appear to be promising candidates for accurate calculation of properties for laser-coolable molecules.