High-accuracy calculations of the ground, 1 ¹A ₁′, and the 2 ¹A₁′,2 ³A₁′, and 1 ¹E′, excited states of H₃⁺

Accurate variational Born-Oppenheimer calculations of the 1 ¹A₁′, 2 ¹A₁′,2 ³A₁′, and 1 ¹E′ states of the H3+ ion at the ground-state equilibrium geometry are reported. The wave functions of the states are expanded in terms of explicitly correlated spherical Gaussian functions with shifted centers. In the variational optimization the analytical gradient of the energy with respect to the nonlinear exponential parameters of the Gaussians has been employed. The energies obtained in the calculations are the best variational estimates ever calculated for the four states. One-electron densities for the states, as well as a D3h -restricted potential energy surface of the ground state calculated around the equilibrium geometry, are also presented and discussed.