Spectroscopic properties of the bound n=3 states of H-2(+)

Spectroscopic properties are determined for the six bound electronic states of H-2(+) that correlate as nuclear separation R --> infinity with a proton and a hydrogen atom in an n=3 state. Two antibonding orbitals 5g pi(g) and 6h sigma(u) have significant potential wells and an infinite number of bound vibrational states due to strongly attractive pole-dipole leading multipole terms. Vibrational-rotational eigenenergies are reported for three angular momentum J values for each bound state. Coefficients up to a(6) are listed for Dunham power-series expansions of the vibrational potentials V(R) about the equilibrium separations R(e). The higher a coefficients come almost entirely from the nuclear Coulomb repulsion only for the 3d delta(g) state, the one state that is lowest of its symmetry type and is therefore not perturbed from below. Dunham Y-ij are determined also; the leading vibrational Y-10, rotational Y-01, and anharmonicity \Y-20\ constants are very small due to the very broad potential wells and large values of R(e) for all six n=3 electronic states. For five of the six states, Y-00 is negative and therefore the vibrational quantum number v(e) at the potential minimum is >-1/2. The wavelength range of the bound-bound (n=3)<->(n=2)(2)(+) transitions is 3800-9700 Angstrom; many unidentified diffuse interstellar bands have been reported in this range. (C) 1996 American Institute of Physics.