Ab initio calculation on the analytic potential energy functions for the state a3Σu+ and the state b3Πu of spin-aligned trimer 7Li2

The energies, equilibrium geometries and harmonic frequencies of the triplet excited states (a(3)Sigma(+)(u) and b(3)Pi(u)) of spin-aligned trimer Li-7(2) are firstly calculated by using a symmetry adapted cluster-configuration interaction method. The potential curves for the two excited states have least squares fitted by the Murrell-Sorbie function. The spectroscopic data (B-e, alpha(e), omega(e), and omega(e)chi(e),) and the force constants (f(2), f(3) and f(4)) are calculated. It is found that the spin-aligned triplet excited state b(3)Pi(u) is more stable than the ground state X-1 Sigma(+)(g), and that the Murrell-Sorbie function form is suitable not only for the ground state but also for the spin-aligned triplet excited states. Comparison between the theoretical determinations of dissociation energies, equilibrium interatomic distances and harmonic frequencies with the experimental data about a(3)Sigma(+)(u) and b(3)Pi(u) clearly shows that the present work represents a significant improvement in agreement between theories and experiments.