Jankowski Piotr, Szalewicz Krzysztof
Department of Quantum Chemistry, Institute of Chemistry, Nicholaus Copernicus University, Toruń, Poland.
J Chem Phys. 2005 Sep 8;123(10):104301. doi: 10.1063/1.2008216.
A new four-dimensional intermolecular potential-energy surface for the H(2)-CO complex is presented. The ab initio points have been computed on a five-dimensional grid including the dependence on the H-H separation (the C-O separation was fixed). The surface has then been obtained by averaging over the intramolecular vibration of H(2). The coupled-cluster supermolecular method with single, double, and noniterative triple excitations has been used to calculate the interaction energy. The correlation part of the interaction energy has been obtained from extrapolations based on calculations in a series of basis sets. An analytical fit of the ab initio potential-energy surface has the global minimum of -93.049 cm(-1) at the intermolecular separation of 7.92 bohr for the linear geometry with the C atom pointing toward the H(2) molecule. For the other linear geometry, with the O atom pointing toward H(2), the local minimum of -72.741 cm(-1) has been found for the intermolecular separation of 7.17 bohr. The potential has been used to calculate the rovibrational energy levels of the para-H(2)-CO complex. The results agree very well with those observed by McKellar [A. R. W. McKellar J. Chem. Phys. 108, 1811 (1998)]: the discrepancies are smaller than 0.1 cm(-1). The calculated dissociation energy is equal to 19.527 cm(-1) and significantly smaller than the value of 22 cm(-1) estimated from the experiment. Predictions of rovibrational energy levels for ortho-H(2)-CO have also been done and can serve as a guidance to assign recorded experimental spectra. The interaction second virial coefficient has been calculated and compared with the experimental data.
提出了一种新的H₂-CO复合物的四维分子间势能面。从头算点是在一个五维网格上计算的，其中包括对H-H间距的依赖性（C-O间距固定）。然后通过对H₂的分子内振动进行平均得到该势能面。采用含单、双和非迭代三激发的耦合簇超分子方法计算相互作用能。相互作用能的相关部分是根据一系列基组计算的外推结果得到的。从头算势能面的解析拟合在分子间间距为7.92玻尔的线性构型下，全局最小值为-93.049 cm⁻¹，C原子指向H₂分子。对于另一种线性构型，O原子指向H₂，在分子间间距为7.17玻尔时发现局部最小值为-72.741 cm⁻¹。该势能已用于计算仲-H₂-CO复合物的振转能级。结果与麦凯勒 [A. R. W. 麦凯勒，《化学物理杂志》108, 1811 (1998)] 观察到的结果非常吻合：差异小于0.1 cm⁻¹。计算得到的解离能为19.527 cm⁻¹，明显小于根据实验估计的22 cm⁻¹的值。还对正-H₂-CO的振转能级进行了预测，可作为确定记录的实验光谱的指导。计算了相互作用第二维里系数并与实验数据进行了比较。
