Ab initio relativistic treatment of the a3Π - X1Σ+, a′3Σ+ - X1Σ+ and A1Π - X1Σ+ systems of the CO molecule

The spin-forbidden a(3)Pi - X-1 Sigma(+), a'3 Sigma(+) - X-1 Sigma(+) and spin-allowed A1 Pi - X-1 Sigma(+) electronic transitions dipole moments of carbon monoxide have been ab initio studied in the framework of multi-reference Fock space coupled cluster method combined with the finite-field approach and the generalized relativistic pseudo-potential model for the effective introducing the relativity in all-electron correlation treatment. Radiative lifetimes, tau(i)(v';, J'), of the upper i is an element of [a(3)Pi, A(1)Pi] states were evaluated as a function of vibrational, v', and rotational, J', quantum numbers. The tau(a)-values derived for the triplet a(3)Pi(1) (0, 1) and a(3)Pi(2) (0, 2) states at the highest level of computation were found to be 2.59 and 142 ms, which are near perfect agreement with their best experimental counterparts (J. J. Gilijamse, et al., J. Chem. Phys., 127, 221102 (2007)). The intercombination a - X, a' - X transition probabilities were numerically proved to be proportional to alpha(2), where alpha = e(2) /(h) over barc is the fine structure constant. (c) 2021ElsevierLtd. Allrightsreserved.