Department of Chemistry, Murray State University, Murray, Kentucky 42071, United States.
J Phys Chem A. 2012 Jan 26;116(3):1069-76. doi: 10.1021/jp2088753. Epub 2012 Jan 13.
This work presents the first investigation on the intermolecular potential energy surface of the ground electronic state of the O2(-)(2Πg)-H2(1Σg(+)) complex. High level correlated ab initio calculations were carried out using the Hartree-Fock spin-unrestricted coupled cluster singles and doubles including perturbative triples correction [RHF-UCCSD(T)]/aug-cc-pVXZ levels of calculations, where XZ = DZ, TZ, QZ, and 5Z. Results of full geometry optimization and the intermolecular potential energy surface (IPES) calculations show four equivalent minimum energy structures of L-shaped geometry with Cs symmetry at equilibrium along the 2A″ surface of the complex. For these equilibrium minimum energy structures, the most accurate value for the dissociation energy (De) was calculated as 1407.7 cm(-1), which was obtained by extrapolating the counterpoise (CP) corrected De values to the complete basis set (CBS) limit. This global minimum energy structure is stabilized by an ion-induced-dipole hydrogen bond. Detailed investigations of the IPES show that the collinear structure is unstable, while the C2v geometries present saddle points along the 2A″ surface. The barrier height between the two equivalent structures that differs in whether the hydrogen-bonded hydrogen atom is above or below the axis that connects centers of masses of the H2 and O2(-) moieties within the complex was calculated as 70 cm(-1). This suggests that the complex exhibits large amplitude motion. The barrier height to rotation of the H2 moiety by 180° within the complex is 1020 cm(-1). Anharmonic oscillator calculations predicted a strong H-H stretch fundamental transition at 3807 cm(-1). Results of the current work are expected to stimulate further theoretical and experimental investigations on the nature of intermolecular interactions in complexes that contain the superoxide radical and various closed-shell molecules that model atmospheric and biological molecules. These studies are fundamental to understanding the role of the O2(-) anion in chemistry in the atmosphere and in biological systems.
这项工作首次研究了基电子态的 O2(-)(2Πg)-H2(1Σg(+)) 复合物的分子间势能面。使用 Hartree-Fock 非限制单双激发耦合簇加上微扰三激发修正 [RHF-UCCSD(T)]/aug-cc-pVXZ 计算水平进行了高精度相关 ab -initio 计算，其中 XZ = DZ、TZ、QZ 和 5Z。全几何优化和分子间势能面 (IPES) 计算的结果表明，在复合物的 2A″ 表面上，沿 Cs 对称的 L 形几何有四个等效的最低能量结构。对于这些平衡最低能量结构，通过将平衡校正 (CP) De 值外推到完全基组 (CBS) 极限，计算出最准确的离解能 (De) 值为 1407.7 cm(-1)。这个全局最低能量结构由离子诱导偶极氢键稳定。对 IPES 的详细研究表明，共线结构不稳定，而 C2v 几何在 2A″ 表面上呈现鞍点。在复合物中，氢原子是否在连接 H2 和 O2(-) 部分质心的轴上方或下方不同的两个等效结构之间的氢键的高度计算为 70 cm(-1)。这表明复合物表现出大振幅运动。在复合物中，H2 部分旋转 180°的势垒高度为 1020 cm(-1)。非谐振荡器计算预测了在 3807 cm(-1)处的强 H-H 伸缩基频跃迁。目前工作的结果预计将激发对含有超氧化物自由基和各种闭壳分子的复合物中分子间相互作用性质的进一步理论和实验研究。这些研究对于理解 O2(-)阴离子在大气和生物系统中的化学作用具有重要意义。
