MULTIMODE quantum calculations of vibrational energies and IR spectrum of the NO~+(H_2O) cluster using accurate potential energy and dipole moment surfaces

摘要

A new, full (nine)-dimensional potential energy surface and dipole moment surface to describe the NO~+(H_2O) cluster is reported. The PES is based on fitting of roughly 32 000 CCSD(T)-F12/aug-ccpVTZ electronic energies. The surface is a linear least-squares fit using a permutationally invariant basis with Morse-type variables. The PES is used in a Diffusion Monte Carlo study of the zero-point energy and wavefunction of the NO~+(H_2O) and NO~+(D_2O) complexes. Using the calculated ZPE the dissociation energies of the clusters are reported. Vibrational configuration interaction calculations of NO~+(H_2O) and NO~+(D_2O) using the MULTIMODE program are performed. The fundamental, a number of overtone, and combination states of the clusters are reported. The IR spectrum of the NO~+(H_2O) cluster is calculated using 4, 5, 7, and 8 modes VSCF/CI calculations. The anharmonic, coupled vibrational calculations, and IR spectrum show very good agreement with experiment.Mode coupling of the water “antisymmetric” stretching mode with the low-frequency intermolecular modes results in intensity borrowing.