Spectra of N2-HF from symmetry-adapted perturbation theory potential

Symmetry-adapted perturbation theory has been used to calculate the interaction energy for the N-2-HF van der Waals complex at two H-F separations corresponding to average values for v(HF) = 0 and v(HF) = 3 vibrational states and the N-N separation corresponding to v(N2) = 0. The total of 228 and 197 grid points have been computed for the v(HF) = 0 and v(HF) = 3 case, respectively. A basis set containing 119 spdf-symmetry orbitals and including bond functions has been used. An analytical fit of the four-dimensional ab initio potential energy surface at the H-F separation corresponding to v(HF) = 0 has a global minimum depth D-e of 762.4 cm(-1) at the intermolecular separation R = 6.73 bohr for the linear geometry with the H atom pointing towards the N-2 molecule. The surface corresponding to the v(HF) = 3 vibrational state has D-e of 897.9 cm(-1) at R = 6.71 bohr and the same orientation of HF relative to N-2 as in the v(HF) = 0 case. Exact quantum rovibrational calculations have been performed on both surfaces and the rotational constants and the lowest rovibrational frequencies of the complex have been compared to experimental data. The agreement between theory and experiment for v(HF) = 0 potential is substantially better than achieved previously, while for the v(HF) = 3 state our results constitute the first theoretical prediction. (C) 2001 American Institute of Physics.