Theoretical prediction of the contact distance dependence of the electron transfer reactivity of the ClO/ClO⁻ coupling system

Abstract

ABSTRACT:On the basis of the structures and properties of the ClO/ClO Ϫ system obtained at the density functional theory (DFT) (UB3LYP) level, employing the 6-311ϩG(3df ) standard basis set, the electron transfer reactivity of this system is investigated. The results indicate that there are five possible stable coupling complexes that correspond to the generous minima on the global potential energy surfaces (PES). The most stable coupling complex is planar EC4, in which there is a OOO linkage with two trans-Cl atoms. Their stabilization energies are calculated to be 20.57 (EC1: C 1 ), 20.54 (EC2: C 2 , 2 B), 20.69 (EC3: C 1 ), 20.70 (EC4: C s , 2 AЈ), and 20.69 (EC.5: C 2h , 2 B u ) kcal/ mol at the B3LYP/6-311ϩG(3df ) level; with the correction of the basis set superposition error (BSSE), the stability order of these encounter complexes is EC4 Ͼ EC.5 Ͼ EC3 Ͼ EC1 Ͼ EC2. Based on the five encounter complexes, five coupling modes are designed for the study of the electron transfer reactivity of this system. The dissociation energy curves at the activated states and the corresponding activation energies of these five coupling modes are obtained and are compared at the B3LYP/6-311ϩG(3df ) and MP2/ 6-311ϩG* levels. The inapplicability of DFT methods has also been discussed in this article in predicting the energy curves, especially with a long contact distance, in which DFT methods give the abnormal behavior for the dissociations of the complexes caused by the "inverse symmetry breaking" problem. On the basis of the golden rule of the time-dependent perturbation theory, the electron transfer reactivity and the contact distance dependence of the various electron transfer kinetics parameters (e.g., activation energy, coupling matrix element) have been analyzed at the UMP2(full)/6-311ϩG* level. The electron transfer can take place over a range of contact distances, but the most effective coupling distance corresponds to only a small range. The coupling orientation analyses also indicate that the most favorable coupling mode to the electron transfer does not always correspond to the most stable encounter complex mechanism. Some highly energetic coupling modes are more favorable for the electron transfer.