Explicitly correlated <i>ab initio</i> potential energy surface and predicted rovibrational spectra for H2O–N2 and D2O–N2 complexes
Lu Wang, Xiaolong Zhang, Yu Zhai, Marcel Nooijen, Hui Li
Abstract
An ab initio intermolecular potential energy surface (PES) for the van der Waals complex of H2O–N2 that explicitly incorporates the intramolecular Q2 bending normal mode of the H2O 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 ν2(H2O) = 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−1 for interaction energies less than 2000.0 cm−1. The resulting vibrationally averaged PESs provide good representations of the experimental microwave and infrared data: for microwave transitions of H2O–N2, the rms discrepancy is only 0.0003 cm−1, and for infrared transitions of the A1 symmetry of the H2O(ν2 = 1 ← 0)–N2, the rms discrepancy is 0.001 cm−1. The calculated infrared band origin shifts associated with the ν2 bending vibration of water are 2.210 cm−1 and 1.323 cm−1 for H2O–N2 and D2O–N2, respectively, in good agreement with the experimental values of 2.254 cm−1 and 1.266 cm−1. The benchmark tests and comparisons of the predicted spectral properties are carried out between CCSD(T)-F12a and CCSD(T)-F12b approaches.