A Four-dimensional Potential Energy Surface And Predicted Spectra For Ar-D₂O:v₂ Normal Mode Dependence

Water molecule can form complexes with other water molecules and molecules of other compounds. These complexes exist extensively in solution phase chemistry and biological processes. The study of intermolecular interaction of these complexes is of vital importance to understand the processes from the microscopic level. For this reason, the simple systems formed by water molecules and rare gas (Rg) atoms have received continuous attention.In this paper, we report a four-dimensional potential energy surface (PES) of the Ar-D2O complex and predicted spectra in the v2 bending region of D2O.The main results are listed as follow:(1)All ab initio calculations are performed with CCSD(T) method with a large basis set(3s3p2dlf) supplemented bond functions. A total of 11466 grid-points are chosen for the potential energy calculations.The interpolating moving least square method, the cubic spline interpolation method and an eighth-order polynomial interpolation method are used to construct a four dimensional potential energy surface (PES).(2)For application in theoretical explanation of infrared spectra, two vibrationally averaged PESs with the D2O molecule at both the ground and the first excited vibrational states are generated by integration over the Q2 normal coordinate. The vibrationally averaged Foo PES has a global minimum with a well depth of-139.2cm-1 at R=6.90α0,φ=0.0° and θ=14.25°.The global minimum structure is consistent with that of AW2 PES except for smaller well depth by roughly 2.5%.The V11 PES has a similar structure as V00 PES. The global minimum, which locates at K=6.84α0,φ=0.0° and θ=80.05° with well depth of -140.55cm-1,a minor smaller with those of V00PES. Geometries with the Ar in the molecular plane (φ=0.0°) are more favorable than out of plane structures.(3)A self-written FORTRAN code is used to calculate the rovibrational energy levels. The theoretical frequencies for rotational and VRT spectra of Ar-D2O in V00PES and 104 infrared transitions of Π111(v2=1)←∑000, ∑111(v2=1)←∑000, Π110(v2=1)←∑101 and Π101(v2=1) ←∑101 of Ar-D2O complex are in good agreement with the available experimental values.