Accurate theoretical study on the ground and first-excited states of Na2: potential energy curves, spectroscopic parameters, and vibrational energy levels

Potential energy curves (PECs) for the ground and first-excited electronic states of Na-2 are obtained by fitting the ab initio energies calculated at the MRCI(Q)/aug-cc-pVXZ (X = T, Q, 5) level of theory, which are subsequently extrapolated to the complete basis set limit. The relativistic effect and core-valence correlation are also considered. The PECs are accurate at both short and long internuclear distances with the root-mean-squared deviations being 0.72 cm(-1) for Na-2(X-1 Sigma(+)(g)) and 0.36 cm(-1) for Na-2 (a(3)Sigma(+)(u)). Utilizing the obtained PECs, we calculate the spectroscopic parameters, vibrational energy levels, classical turning points, inertial rotation, and centrifugal distortion constants, which are in good agreement with other theoretical and experimental work.