Wheeler Steven E, Simmonett Andrew C, Schaefer Henry F
Center for Computational Chemistry, University of Georgia, Athens, GA 30602, USA.
J Phys Chem A. 2007 May 24;111(20):4551-5. doi: 10.1021/jp0712046. Epub 2007 Apr 20.
There are inconsistencies among previously reported Renner-Teller bending frequencies for the approximately A 2Pi state of OCS+. To resolve these controversies, we have computed vibrational frequencies using high-level excited electronic state ab initio equation-of-motion coupled cluster methods. On the basis of equation-of-motion coupled cluster theory including single, double, and iterative inclusion of partial triple excitations (EOM-CC3) paired with the correlation-consistent polarized valence quadruple-zeta basis set (cc-pVQZ), we predict harmonic bending frequencies of 364 and 401 cm-1 for the A' and A" components of approximately A 2Pi OCS+, respectively. Particularly for the upper Renner-Teller component, these results are lower than the theoretical predictions of 370 and 459 cm-1 reported by Chen, Hochlaf, Rosmus, He, and Ng [J. Chem. Phys. 2002, 116, 5612]. Instead, the presently computed bending frequencies are more consistent with the experimentally derived average value of 357 +/- 5 cm-1 recently reported by Sommavilla and Merkt [J. Phys. Chem. A 2004, 108, 9970], lending credence to the spectral assignments made in this later work. The two components of the Renner-Teller bending frequencies of approximately X 2Pi OCS+ are similarly predicted to be 396 and 453 cm-1. Anharmonicity constants arising from a quartic force field computed at the cc-pVQZ EOM-CC3 level of theory are given, to provide a more complete characterization of the potential energy surface of the approximately A 2Pi state of OCS+.
对于OCS⁺的近似A²Π态，先前报道的伦纳 - 泰勒弯曲频率存在不一致之处。为了解决这些争议，我们使用高级激发电子态从头算运动方程耦合簇方法计算了振动频率。基于包含单、双激发以及部分三激发的迭代包含的运动方程耦合簇理论（EOM - CC3），并结合相关一致极化价四重zeta基组（cc - pVQZ），我们预测近似A²Π OCS⁺的A'和A''分量的谐波弯曲频率分别为364和401 cm⁻¹。特别是对于较高的伦纳 - 泰勒分量，这些结果低于Chen、Hochlaf、Rosmus以及He和Ng [《化学物理杂志》2002年，116卷，5612页]报道的370和459 cm⁻¹的理论预测值。相反，目前计算出的弯曲频率与Sommavilla和Merkt [《物理化学杂志A》2004年，108卷，9970页]最近报道的实验得出的平均值357 ± ５ cm⁻¹更为一致，这为该后期工作中的光谱归属提供了可信度。近似X²Π OCS⁺的伦纳 - 泰勒弯曲频率的两个分量同样被预测为396和453 cm⁻¹。给出了在cc - pVQZ EOM - CC3理论水平下计算的四次力场产生的非谐性常数，以更完整地表征OCS⁺近似A²Π态的势能面。
