Spectra of N-2-HF from symmetry-adapted perturbation theory potential

Symmetry-adapted perturbation theory has been used to calculate the interac tion energy for the N-2-HF van der Waals complex at two H-F separations cor responding 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 19 7 grid points have been computed for the v(HF) = 0 and v(HF) = 3 case, resp ectively. A basis set containing 119 spdf-symmetry orbitals and including b ond functions has been used. An analytical fit of the four-dimensional ab i nitio 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 s eparation R = 6.73 bohr for the linear geometry with the H atom pointing to wards the N-2 molecule. The surface corresponding to the v(HF) = 3 vibratio nal 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 rovibrationa l calculations have been performed on both surfaces and the rotational cons tants and the lowest rovibrational frequencies of the complex have been com pared to experimental data. The agreement between theory and experiment for v(HF) = 0 potential is substantially better than achieved previously, whil e for the v(HF) = 3 state our results constitute the first theoretical pred iction. (C) 2001 American Institute of Physics.