Explicitly correlated ab initio potential energy surface and predicted rovibrational spectra for HO-N and DO-N complexes.

An ab initio intermolecular potential energy surface (PES) for the van der Waals complex of HO-N that explicitly incorporates the intramolecular Q bending normal mode of the HO monomer is presented. The electronic structure computations have been carried out at the explicitly correlated coupled cluster theory [CCSD(T)-F12] with an augmented correlation-consistent triple zeta basis set and an additional bond function. Analytic five-dimensional intermolecular PESs for ν(HO) = 0 and 1 are obtained by fitting to the multi-dimensional Morse/long-range potential function form. These fits to 40 890 points have the root-mean-square (rms) discrepancy of 0.88 cm for interaction energies less than 2000.0 cm. The resulting vibrationally averaged PESs provide good representations of the experimental microwave and infrared data: for microwave transitions of HO-N, the rms discrepancy is only 0.0003 cm, and for infrared transitions of the A symmetry of the HO(ν = 1 ← 0)-N, the rms discrepancy is 0.001 cm. The calculated infrared band origin shifts associated with the ν bending vibration of water are 2.210 cm and 1.323 cm for HO-N and DO-N, respectively, in good agreement with the experimental values of 2.254 cm and 1.266 cm. The benchmark tests and comparisons of the predicted spectral properties are carried out between CCSD(T)-F12a and CCSD(T)-F12b approaches.