The calculation of highly excited bound-state energy levels for a triatomic molecule by using three-arrangement basis sets and contracted basis functions

The rovibrational energy levels of the nonrotating H+3 molecular ion have been calculated using a basis set defined in three-arrangement Jacobi coordinates. Energy levels corresponding to the A′1 symmetry are reported up to 22 600 cm−1 above the potential energy minimum and are converged to within 1.8 cm−1, energy levels in the A2 symmetry are reported up to 28 800 cm−1 and are converged to within 0.7 cm−1, and energy levels in the E′ symmetry are reported up to 24 300 cm−1 and are converged to within 1.8 cm−1. The maximum deviation of the reported results from the results of Carter and Meyer [J. Chem. Phys. 93, 8902 (1990)] is about 2 cm−1, and most of the results agree to within 1 cm−1. An advantage to our basis set is that it can represent the full D3h symmetry of this system, and thus the energy levels are assigned to the correct symmetry group unambiguously. In order to improve computational efficiency, contracted basis functions were formed using a successive diagonalization-truncation procedure.