Ab Initio Study of the Intermolecular Potential Energy Surface in the Ion-Induced-Dipole Hydrogen-Bonded O2鈥?/sup>(X2螤g)鈥揌2(X1危g<
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- 作者：Wafaa M. Fawzy
- 刊名：The Journal of Physical Chemistry A
- 出版年：2012
- 出版时间：January 26, 2012
- 年：2012
- 卷：116
- 期：3
- 页码：1069-1076
- 全文大小：701K
- 年卷期：v.116,no.3(January 26, 2012)
- ISSN：1520-5215
文摘
This work presents the first investigation on the intermolecular potential energy surface of the ground electronic state of the O2鈥?/sup>(2螤g)鈥揌2(1危g+) complex. High level correlated ab initio calculations were carried out using the Hartree鈥揊ock 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鈥?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鈥?, 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鈥?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鈥?/sup> moieties within the complex was calculated as 70 cm鈥?. This suggests that the complex exhibits large amplitude motion. The barrier height to rotation of the H2 moiety by 180掳 within the complex is 1020 cm鈥?. Anharmonic oscillator calculations predicted a strong H鈥揌 stretch fundamental transition at 3807 cm鈥?. 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鈥?/sup> anion in chemistry in the atmosphere and in biological systems.