Ab initio calculation of the a 3Σ+u interaction potential and vibrational levels of 7Li2

The interaction potential of the lowest triplet excited state, a 3Σ+u, for Li2 has been calculated using the ab initio method, QCISD(T) and the correlation-consistent valence polarised quintuple zeta basis set, cc-pV5Z. Equilibrium constants and vibrational levels for 7Li2 are in good agreement with experimental determinations. The a 3Σ+u energy curve for Li2 is characterised at the QCISD(T, full)/cc-pV5Z level of theory by the parameters De, Do, Re, ωe and ωexe which are found to be 334.145 cm−1, 301.989 cm−1, 4.1686 Å, 65.400 cm−1 and 3.208 cm−1, respectively.