Theoretical Studies Of The Potential Energy Surface And Ro-vibrational Spectra For Kr-H₂O, Ne-H₂S And Ar-H₂S

The structures and dynamics of van der Waals (vdW) complexes have attracted considerable attentions in both experimental and theoretical studies, because the vdW intermolecular interaction forces play an important role in many important physical, chemical and biological processes. The high-resolution spectroscopy of these complexes provides useful information on the intermolecular potential energy surface (PES) and dynamics of such weakly bound molecules. Due to the weak intermolecular forces in vdW complexes, the intermolecular vibrational modes have low frequencies and large amplitudes, so that the global potential energy surface is required to determine the rovibrational bound states and predict the spectra. On the other hand, the quality of the PES can also be justified by comparing the predicted spectra with the high-resolution spectra of the complexes. In this work, we chose KX-H2O, Ne-H2S and Ar-H^S as the representative vdW complexes for investigation, which include the important molecules in atmosphere and life bodies. The H2O and H2S molecules are treated as rigid rotor, and the high-precesion three-dimensional potential energy surfaces for these three complexes are constructed, and the rotational spectra are interpreted well, such as rotational transition frequencies, averaged structural parameters and nuclear quadrupole coupling constants. The theoretical method on this paper is useful for the theoretical studies of these vdW complexes.1. Base on the theretical studies of vdW complexes between rare-gas atoms and linear molecules (CO2and N2O), we develop a new set of suitable methods for the theoretical studies of vdW complexes between rare-gas atoms and nonlinear H2X (X=O, S) molecules by choosing a new set of coordinates, Hamiltonian and basis set, and developing the calculation formula and fortran codes for the rovibratonal energy levels.2. We report a three-dimensional ab initio intermolecular potential energy surface for the Kr-H20complex. The intermolecular potential energies were evaluated at the CCSD(T) level with a large basis set including bond functions. The potential has a planar H-bond global minimum, two planar first-order and one second-order saddle points. The combined radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm were employed to calculate the rotational transiton frequencies, averaged structural parameters and nuclear quadrupole coupling constants χaa(17O) and χaa(D) for the ground and first vibrational excited states (∑(000) and∑(101) of sixteen isotopic species of the Kr-H2O complexes, and the free-rotation extents of H2O subunit within the complexes on the two states were also analyzed. The theoretical results are all in good agreement with the available experimental values, and the theoretical isotopic shift reflects the same tendency with the experimental observations.3. We report a three-dimensional ab initio intermolecular potential energy surface for Ne-H2S and Ar-H2S using a supermolecular approach at the CCSD(T) level. The two potential both character a planar T-shaped global minimum and one planar local minimum, and two planar first-order and one second-order saddle points were also indentified. The well depth of the T-shaped global minimum for Ne-H2S and Ar-H2S is71.57cm-1and177.48cm-1respectively. The rovibrational energy levels for eight isotopic species of Ne-H2S and four isotopic species of Ar-H2S were calculated employing the combined radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm, and the rotational transiton frequencies for the ground and first vibrational excited states (∑(000) and∑(101)) were also determined. Our calculated transition frequencies are in good accord with the observed values with the deviations within0.015cm-1, and the theoretical isotopic shift reflects the same tendency with the experimental observations. We also determined the averaged structural parameters and the properties of the probability densities for∑(000) and∑(101) states of different isotopic species of Ne-H2S and Ar-H2S, and analyzed the free-rotation extents of H2S and D2S subunit within Ne-H2S, Ne-D2S, Ar-H2S and Ar-D2S complexes on the∑(000) and∑(101) states. The free-rotation extents of H2S and D2S subunit has the following order:∑(000)(Ne-H2S)>∑(000)(Ne-D2S)>∑(101)(Ne-H2S)>∑(101)(Ne-D2S) for Ne-H2S and Ne-D2S, and∑(000)(Ar-H2S)>∑(101)(Ar-H2S)>∑(Ooo)(Ar-D2S)>∑(101)(Ar-D2S) for Ar-H2S and Ar-D2S.The ab initio PES and theoretical methods on this paper are suitable for the theoretical studies of vdW complexes between rare-gas atoms and nonlinear H2X (X=O, S) molecules. The predicted rotational spectra based on our calculated potentials are in excellent agreement with the available experiment data, which testifies the accuracy of the new potentials and the theoretical methods. Our theoretical studies can predict and assign the energy levels, provide useful information about vdW molecular dynamics, and reveal the nature of the intermolecular interactions.