The Study Of The Potential Energy Surface And Bound States Of The Kr-OCS Complex

Recent years have witnessed a remarkable growth in the experimental andtheoretical interest in the spectroscopy of the rare gas （Rg） atoms with theOCS molecule（-OCS） since OCS has proven to be an ideal probe ofultracold nanodroplets, a topic of intense recent interest in chemicalphysics. Such studies have been aimed at understanding the nature of theintermolecular potentials and dynamics of these weakly bound molecules.In this work, we investigated the potential energy surface and energylevel of bound states of the Kr-OCS system. The supermolecular couplingcluster theory CCSD （T） method was adopted. We used the atomic centerGaussian base group. For Kr atoms, the relativistic effect of the effectivecore potential （ECP） base group of aug-cc-pVQZ-PP was considered,and the base group of aug-cc-pVTZ was adopted to O, C and S atom. Thebase was further augmented with midbond function （3s3p2d1f） tocalculate the interaction potential of system under supermolecularapproach. The energy levels of Kr-OCS complex were obtained bysolving the shr dinger equation. The transition frequency and spectraconstants are predicted and compared with experimental counterparts.The main results are listed as follow: （1） We calculated the interaction potential of Kr-OCS complex at228configurations fixed OCS molecules at its equilibrium position. Theparametric model potential was used to fit the ab initio values at discretedconfigurations. The potential parameters were determined by nonlinearleast squares method. We thus obtained the analytic two dimensionalpotential energy surface V（R,θ） of the Kr-OCS complex firstly. It isclear that the potential is characterized by a global T-shaped minimumand one local collinear minimum. The global minimum is-270.73cm^-1,found at a geometry with R=7.146a₀and=105.0°. However, the globalminimum was quasilinear structure.（2） Using the two dimensional potential energy surface V（R,θ） andsolving the corresponding Schr dinger Equation numerically, the energylevel structure of three isotopomers⁸²Kr–OCS,⁸⁴Kr–OCS and86Kr–OCSwas obtained. The calculated microwave spectrum of the transitionfrequencies and spectroscopic constants of the three isotopomers are ingood agreement with the experimental values. For example, most of thecalculated frequencies are within0.005of the observed values andthe root mean squares error is0.0044,0.0032and0.0042for threeisotopomers respectively.（3） In order to explain the experimental infrared spectrum involvingantisymmetric stretching vibration of the monomer OCS molecule, wepresent the three-dimensional potential energy surface V（Q3,R,θ） including theQ₃antisymmetric stretching vibration normal mode. Atfirst, the relation ofQ（i3i=1-7）with bond length of OCS molecules weredetermined. Then, seven analytic two-dimensional potentials modelV（Qⁱ₃,R,θ） were calculated and fitted. The seven model potentials are usedto construct the three-dimensional potential energy surface byinterpolating alongQ3using a sixth-order polynomial.（4） Within the adiabatic approximation, two vibrationally averagedpotentials with the OCS molecule at both the ground（v30） and the frst（v₃1） vibrational excited states were generated from the integration ofthe three-dimensional potential V（,R,θ） over theQ3coordinate. Thesetwo potentials were further used to calculate the correspondingrovibrational levels of complex. For66infrared transitions theroot-mean-square discrepancy is about0.011cm^-1. The calculated infraredband origin shift, bending ground frequency, and molecular constantsassociated with thev3nomal mode of OCS are all in good agreementwith the experimental values.