On the Chaperon Mechanism: Application to ClO + ClO (+N2) ClOOCl (+N2)
详细信息 查看全文
- 作者：Jingyao Liu ; John R. Barker
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：September 6, 2007
- 年：2007
- 卷：111
- 期：35
- 页码：8689 - 8698
- 全文大小：242K
- 年卷期：v.111,no.35(September 6, 2007)
- ISSN：1520-5215
文摘
The dynamics of the ClO + ClO (+N2) radical complex (or chaperon) mechanism is studied by electronicstructure methods and quasi-classical trajectory calculations. The geometries and frequencies of the stationarypoints on the potential energy surface (PES) are optimized at the B3LYP/6-311+G(3df) level of theory, andthe energies are refined at the CCSD(T)/6-311+G(3df) (single-point) level of theory. Basis set superpositionerror (BSSE) corrections are applied to obtain 1.5 kcal mol-1 for the binding energy of the ClO·N2 van derWaals (VDW) complex. A model PES is developed and used in quasi-classical trajectory calculations toobtain the capture rate constant and nascent energy distributions of ClOOCl* produced via the chaperonmechanism. A range of VDW binding energies from 1.5 to 9.0 kcal mol-1 are investigated. The anisotropicPES for the ClO·N2 complex and a separable anharmonic oscillator approximation are used to estimate theequilibrium constant for formation of the VDW complex. Rate constants, branching ratios to produce ClOOCl,and nascent energy distributions of excited ClOOCl* are discussed with respect to the VDW binding energyand temperature. Interestingly, even for weak VDW binding energies, the N2 usually carries away enoughenergy to stabilize the nascent ClOOCl*, although the VDW equilibrium constant is small. For strongerbinding energies, the stabilization efficiency is reduced, but the capture rate constant is increasedcommensurately. The resulting rate constants for forming ClOOCl* from the title reaction are only weaklydependent on the VDW binding energy and temperature. As a result, the relative importance of the chaperonmechanism is mostly dependent on the VDW equilibrium constant. For the calculated ClO·N2 binding energyof 1.5 kcal mol-1, the VDW equilibrium constant is small, and the chaperon mechanism is only important atvery high pressures.