Spin-orbit coupling in low-lying electronic states of CuH

Potential energy curves for the low-lying electronic states of CuH have been calculated using the MRCI method with a large active space containing the 3d, 4s, 4p and 3d' orbitals of the copper atom. All electronic states of CuH correlating with the 3d¹⁰ 4s¹ (²S) and 3d⁹ 4s² (²D) states of Cu were included, and spin-orbit corrections were calculated using the MRCI wavefunctions. Potential energy curves were obtained for individual Ω states, and the Einstein A coefficients were computed for the spin-forbidden transitions from the low-lying electronic states to the X¹Σ⁺ ground state. Diagonal and off-diagonal elements of the spin-orbit Hamiltonian matrix were calculated for the X¹Σ⁺, A¹Σ⁺, 1³Σ⁺, 2³Σ⁺, 1¹Π, 1³Π, 1¹Δ and 1³Δ states, and the mixing of vibronic wavefunctions was investigated using the eigenvectors. The available experimental data on vibrational levels of the A¹Σ⁺ excited state of CuH and CuD were combined in a multi-isotopologue Birge-Sponer plot, and the ab initio data on the unobserved vibrational levels were used for a more accurate extrapolation, resulting in a new experimental value for the equilibrium dissociation energy (D_e) of the CuH molecule. The D_e value for the ground state of CuH was determined to be 22 630 ± 250 cm^-1, resulting in D₀ values of 2.686 and 2.720 eV for CuH and CuD, respectively. Therefore, new experimental values for the bond dissociation enthalpies of CuH and CuD are reported to be 262.9 ± 3 and 266.2 ± 3 kJ mol^-1, respectively.