Investigation on vibrational levels, inertial rotation and centrifugal distortion constants of 7Li2(X1Σg+)

The density-functional theory (B3LYP, B3P86) and the configuration-interaction method (CCSD(T), QCISD) presented in Gaussian03 program package are employed to calculate the equilibrium internuclear distance Re, the harmonic frequency cue and the dissociation energy D-e of Li-7(2) (X-1 Sigma(+)(g)) under a number of basis sets. By comparison with the measurement, the conclusion is that the most accurate R-e, D-e and omega(e) results (0.2698 nm, 1.0487 eV and 346.82 cm(-1), respectively) can be obtained at the CCSD(T)/cc-PVQZ level of theory. The potential energy curve at this level is calculated over a wide internuclear separation range of 0.15 to 2.7 nm at a 0.03 nm step size and is fitted to the analytic Murrell-Sorbie function. With the potential obtained at the CCSD(T)/cc-PVQZ level of theory, the rest spectroscopic parameters (omega(e)chi(e), alpha(e), and B-e) are calculated and the values are 2.648 cm(-1), 0.00702 cm(-1) and 0.6601 cm(-1), respectively, which are in excellent agreement with the experimental ones. By solving the radial Schrodinger equation of nuclear motion, the total number of 41 vibrational states has been found when J = 0 for this X-1 Sigma(+)(g) state. For each vibrational state, the vibrational level, the classical turning point and the inertial rotation constant have been computed, which are in good agreement with the experimental findings. The complete centrifugal distortion constants (D-nu, H-nu, L-nu, M-nu, N-nu and O-nu) are reported for the first time for the first 31 vibrational states when J = 0.