Computational Methods
Geometry optimization calculations and frequency calculations
were carried out using Titan (8). Both B3LYP/ccpVTZ
and LMP2/cc-pVTZ methods were used in the double
bond rotation calculation of trans-2-butene. Multiconfigurational
self-consistent field (MCSCF) calculations
using two models, CAS (2,2) and (4,4), were performed with
Gaussian 03 (9).