PHOTODISSOCIATION DYNAMICS OF HNF - I - AB-INITIO CALCULATION OF GLOBAL POTENTIAL-ENERGY SURFACES, VIBRATIONAL ENERGIES, AND WAVE-FUNCTIONS

Three-dimensional potential energy surfaces for the (X) over tilde (2) A '' and (A) over tilde (2)A' states of HNF are reported in the presen t paper. The ab initio calculations are carried out at the multirefere nce configuration interaction (MRD-CI) level of theory employing a lar ge basis set. The (X) over tilde (2)A '' potential surface possesses a deep potential well. Both surfaces have a bent equilibrium, at approx imately 100 deg for the ground state and at about 125 deg for the exci ted one. The two electronic states become degenerate at the linear geo metry. Variational calculations for the vibrational energies and the c orresponding wave functions have been performed on three-dimensional f itted potential energy surfaces. The first 101 levels of the (X) over tilde (2)A '' state and the lowest 51 levels of the (A) over tilde (2) A' manifold are reported, and their vibrational modes are assigned on the basis of the nodal structure of the corresponding wave functions. The (A) over tilde (2)A' vibrational states consist of well-defined po lyads with polyad quantum number P = 3v(1) + v(2) + v(3) where v(1) - v(3) are the H-N stretching, bending, and N-F stretching quantum numbe rs, respectively. The calculated barrier height, vertical and adiabati c excitation energies, as well as the dissociation limits, agree satis factorily with the available experimental data. This underlines that t he overall accuracy of the potential energy surfaces is good. (C) 1998 American Institute of Physics. [S0021-9606(98)30641-8].