Ab initio calculation on the analytic potential energy functions for the state a³Σ⁺_u and the state b³\Pi_u of spin-aligned trimer ⁷Li₂

The energies, equilibrium geometries and harmonic frequencies of the triplet excited states (a³Σ⁺_u and b³\Pi_u of spin-aligned trimer ⁷Li₂ 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 (f₂, f₃ and f₄ are calculated. It is found that the spin-aligned triplet excited state b³\Pi_u is more stable than the ground state X¹Σ⁺_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 a³Σ⁺_u and b³\Pi_u clearly shows that the present work represents a significant improvement in agreement between theories and experiments.