The vibration-rotation-tunneling levels of N2–H2O and N2–D2O

Abstract

In this paper, we report vibration-rotation-tunneling levels of the van der Waals clusters N2-H2O and N2-D2O computed from an ab initio potential energy surface. The only dynamical approximation is that the monomers are rigid. We use a symmetry adapted Lanczos algorithm and an uncoupled product basis set. The pattern of the cluster's levels is complicated by splittings caused by H-H exchange tunneling (larger splitting) and N-N exchange tunneling (smaller splitting). An interesting result that emerges from our calculation is that whereas in N2-H2O, the symmetric H-H tunnelling state is below the anti-symmetric H-H tunnelling state for both K = 0 and K = 1, the order is reversed in N2-D2O for K = 1. The only experimental splitting measurements are the D-D exchange tunneling splittings reported by Zhu et al. [J. Chem. Phys. 139, 214309 (2013)] for N2-D2O in the v2 = 1 region of D2O. Due to the inverted order of the split levels, they measure the sum of the K = 0 and K = 1 tunneling splittings, which is in excellent agreement with our calculated result. Other splittings we predict, in particular those of N2-H2O, may guide future experiments.

Using monomer vibrational wavefunctions to compute numerically exact (12D) rovibrational levels of water dimer

“…[40][41][42] Similar rigid-monomer calculations have been done for other complexes. [43][44][45][46][47][48][49][50][51][52] Tunneling splittings computed with the rigid-monomer KEO and accurate ab initio PESs agree extremely well with their experimental counterparts, [21] however, it is important to develop tools that enable one to compute the water dimer spectrum without making the rigid-monomer approximation. This is important because 1) the best possible refined water dimer PES must be obtained from an exact calculation and 2) it is only by doing the 12D calculation that it will be possible to compute shifts of intra-monomer frequencies.…”

Computational study of the ro-vibrational spectrum of CO–CO2

“…It has been demonstrated that such calculations are accurate for other Van der Waals dimers. [11][12][13][14] Probability Density (PD) and wavefunction cut plots are used to label the energy levels. We find significant coupling between in-plane and out-of-plane coordinates.…”

Computational study of the rovibrational spectrum of (CO2)2

“…By using an exact ro-vibrational variational method for the intermolecular coordinates and a high-level ab initio potential energy surface (PES), it is possible to compute accurate spectra of Van der Waals dimers. [1][2][3][4][5][6][7][8] In this paper, we apply the same techniques to determine rovibrational energy levels for (CO 2 ) 2 . The spectra of Van der Waals dimers reveal information about interactions between molecules.…”