CH_3F-Ar体系的高精度势能面及预测的振转光谱

An accurate potential energy surface and predicted infrared and microwave spectra for CH_3F-Ar complex

本文在从头算CCSD(T)/AVQZ水平上计算了CH_3F-Ar体系包含CH_3F分子Q_3振动的四维势能面.以摩斯长程势(MLR)为模型,分析的三维高精度分子间势能面通过非线性拟合振动平均的基态(v_3=0)和激发态(v_3=1)的能量而得到.其中对2038个格点拟合的方差仅为0.08 cm-1.我们发现,该体系相互作用能的主要贡献来源于短程的交换排斥能和长程的色散能,势能面有3个极小值点,在θ方向表现出强烈的各向异性,而在φ方向各向异性比较弱.与CH_3F-He体系相比,分子间相互作用较强,分子间相互作用对单个分子的束缚较明显,CH_3F和Ar表现得更像紧束缚的超分子.随后,采用径向离散变量表象(DVR)和角度有限基组表象(FBR)相结合的杂化基函数方法进行展开,用Lanzcos迭代的方法计算了该体系的振转能级,并首次报道了该体系的微波、红外光谱.值得指出的是,由于相互作用比较强,形成的势阱较深,该体系在两个不同的势阱中分别形成了分子间振动基态和激发态,这与CH_3F-He体系中全空间离域的能级态形成鲜明的对比.

Four-dimensional potential energy surfaces（PESs） for CH3F-Ar system that explicitly incorporates dependence on the Q3 stretching normal mode of the CH3F molecule and calculate at CCSD（T）/AVQZ level have been calculated.Based on the Morse/long-range potential function form,the 3-D PESs for v3（CH3F）=0 and 1 are obtained by least-squares fitting the vibrational averaged intermolecular energies.The root-mean-square difference is only 0.08cm^（-1） fitting 2038 pints.We find that the main contribution of the interaction energy of this system come from the short-range exchange-repulsion energy and the long-range dispersion energy.The PESs that have three minimum are very anisotropic in the θ dimension while much weaker in the φ,dimension.The CH3F-Ar complex is more like a tightly bonded super-molecule compared with the CH3F-He system,due to much stronger interaction of CH3F-Ar.The combined radial discrete variable representation/angular finite basis representation methods are used,and Lanczos propagation algorithm is employed to evaluate the rovibrational energy levels.The predicted microwave and infrared spectra are reported for the first time.It＇s interesting to note that there are two sets of vibrational states localized in two different potential well for CH3F-Ar,which forms a sharp contrast to the only delocalized set of vibrational states of CH3F-He.