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

Symmetry-adapted perturbation theory has been used to calculate the interaction energy for the N2–HF van der Waals complex at two H–F separations corresponding to average values for vHF=0 and vHF=3 vibrational states and the N–N separation corresponding to vN2=0. The total of 228 and 197 grid points have been computed for the vHF=0 and vHF=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 vHF=0 has a global minimum depth De of 762.4 cm−1 at the intermolecular separation R=6.73 bohr for the linear geometry with the H atom pointing towards the N2 molecule. The surface corresponding to the vHF=3 vibrational state has De of 897.9 cm−1 at R=6.71 bohr and the same orientation of HF relative to N2 as in the vHF=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 vHF=0 potential is substantially better than achieved previously, while for the vHF=3 state our results constitute the first theoretical prediction.