Explicitly correlated ab initio potential energy surface and predicted rovibrational spectra for H2O-N2 and D2O-N2 complexes.
2020
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.
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