Ab initio rotation-vibration energies and intensities for the H2F+ molecule

In a previous publication [I. D. Petsalakis, G. Theodorakopoulos, J. S. Wright, and I. P. Hamilton, J. Chem. Phys., 92, 2440-2449 (1990)] we reported the ab initio multireference configuration interaction calculation of the three-dimensional potential energy surface of the H2F+ molecule in the ground X ̃1A1 electronic state at 119 nuclear geometries spanning an energy range up to about 50 000 cm-1 above equilibrium. We fitted the 71 points within 33 000 cm-1 of equilibrium to an analytic expression and performed variational calculation of the vibrational energies in Jacobi coordinates using the Discrete Variable Representation and Distributed Gaussian Basis functions (DVR-DGB) technique. In the present paper we examine the effect on the vibrational energies of using a surface obtained by fitting through 52 points within 25 000 cm-1 of equilibrium. We use this surface in a variational calculation of the J = 0, 1, and 2 rotation-vibration energies using the Morse Oscillator Rigid Bender Internal Dynamics Hamiltonian [P. Jensen, J. Mol. Spectrosc., 128, 478-501 (1988); J. Chem. Soc. Faraday Trans. 2, 84, 1315-1340 (1988)]. The vibrational energies obtained are compared with those obtained by the DVR-DGB technique. We also calculate ab initio the dipole moment function and rotation-vibration intensities, and we simulate the ν2 band, which has not yet been observed