Shihai Yan

Theoretical prediction of the state–state correlation among doublet state SNO isomers

Abstract The geometries and the harmonic vibrational frequencies for several SNO doublet state isomers have been predicted at density functional theory levels with a 6-311+G* basis set. Results have indicated that there are nine doublet states (five bent, three nearly linear and one cyclic). The ground state corresponds to a bent 2 A ′ SNO structure. The state–state correlation and the isomerization mechanism are also predicted by searching the transition states and the intrinsic reaction coordinate analysis. Results have indicated that the ground state is the most favorable product. The nearly linear 2 A ″ SNO state may be obtained from the bent 2 A ′ SNO state by electron transition.

Theoretical studies on the contact distance dependence of the electron transfer reactivity of the ClO/ClO+ coupling system

The structures and properties of ClO, ClO+ and their coupling system are studied with ab initio (HF and MP2) and density functional theory (DFT: B3LYP, B3P86, B3PW91) employing the 6-311+G(3df) basis set. Results indicate that there are five possible stable coupling complexes, which correspond to generous minima on the global potential energy surfaces (PES). The most stable coupling complex is EC.3 (Cs, 2A′) in which there is one O–O linkage and two anti-disposed Cl atoms. The stabilization energies are calculated to be 35.78 (EC.1: C2h, 2Bg), 58.34 (EC.2: C2v, 2A2), 61.72 (EC.3: Cs, 2A′), 59.07 (EC.4: C2h, 2Bg) and 25.21 (EC.5: C2h, 2Ag) kcal·mol−1 at the B3LYP/6-311+G(3df) level with correction of the basis set superposition error (BSSE); the stability order of these encounter complexes is EC.3 > EC.4 > EC.2 > EC.1 > EC.5. On the basis of the five encounter complexes, five coupling modes are designed for the electron transfer reactivity of this system, in which the contact distance between the two directly linked atoms is defined as the reaction coordinate. The dissociation energy curves at the activated states and the corresponding activation energies of these five coupling modes are obtained and also are compared at the B3LYP/6-311+G(3df) and MP2/6-311+G* levels. The inapplicability of DFT methods in predicting the energy curves, especially with long contact distances, is also discussed in this paper; the DFT methods give an abnormal behavior for the dissociation of the complexes due to the “inverse symmetry breaking” problem. On the basis of the golden rule of time-dependent perturbation theory, the electron transfer reactivity and the contact distance dependences of the various electron transfer kinetics parameters (the activation energy, the coupling matrix element, etc.) have been analyzed at the MP2(full)/6-311+G* level. The electron transfer can take place over a range of contact distances, but the most effective coupling distance perhaps corresponds to only a small range of distances. The coupling orientation analysis also indicates that the most favorable coupling mode for the electron transfer does not always correspond to the mechanism for the formation of the most stable encounter complex. Some highly energetic coupling modes perhaps favor the electron transfer reaction.

Golden-rule treatment on the ClO/ClO+ electron-transfer system

The structures, properties and electron transfer reactivity of the ClO/ClO+ coupling system are studied in this paper at ab initio (HF and MP2) levels and the density functional theory (DFT: B3LYP, B3P86, B3PW91) levels employing 6311 + G(3df) basis set and on the basis of the golden-rule of the time-dependent perturbation theory. Investigations indicate that the results got from the B3LYP method employing 6-311 + G(3df) basis set is in excellent agreement with the experiment. The activation energies, the stabilization energies and the electronic coupling matrix elements have also been calculated by using the B3LYP/6-311 + G(3df) method, and then the electron transfer rates are determined at this level. The electronic coupling matrix element of EC.6 is very small, only 0.03 kcal/mol, while that of EC.7 is the biggest, being 12.41 kcal/mol, the corresponding electron transfer rate is also the fastest among these seven encounter complexes. The averaged electron transfer rate is about 1.672 X 10(11) M-1 s(-1). It is indicated that the structures optimized by B3LYP method are more reliable than the results got from the other four methods. It also testified that the electronic coupling matrix element is the vital factor that significantly affects the electron transfer rate

Structure analysis of SiSO+ and GeSO+ systems in doublet state at density functional theory and wavefunction-correlated levels

Abstract The geometries and the vibrational frequencies for several SiSO+ and GeSO+ species at doublet state have been predicted at density functional theory level with a 6-311+G* basis set. The detailed bonding character is discussed, and the state–state energy separations of various stable states relative to the ground state are calculated. The ground states are linear Si–OS+ and cyclic GeSO+ for two systems, respectively. Result analysis indicates that the 2 A ″ cyclic state should be classified as the thiosuperoxide, the bent structure and the linear M–OS+ structure have some thiosuperoxide characters, but the linear S–M–O+ may be classified as thio-oxide.