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

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 (2)pi and (2)Delta 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 '(2)Delta(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 A(2)Pi(1/2) <-> X-1(2)Sigma(+)(/2) cycle through the A '(2)Delta(3/2) state by repumping the A '(2)Delta(3/2) state to the B-2 Sigma(+)(1/2) state, which subsequently decays back to X-2 Sigma(+)(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.