Investigation on the potential barrier to internal rotation in molecules-Ab initio calculation and energy partition of the internal rotation barrier in complex molecule H3N-BH3

Abstract

Based on the ab initio/6–31G* calculation, the potential barrier to internal rotation in molecule H3N-BH3 has been studied by means of PD/LSF atomic charge model and Buckingham(exp-6–1) energy partition method. The results indicate that the order of the contributions of the components to the total energy barrier ΔE is |ΔVed|(electrostatic)>|ΔV| (charge transfer)> |ΔVex| (exchange repulsion) > |ΔVdi| (dispersion). For ΔVes there are maxima at θ = 30° and 90°, and a saddle at θ = 60°. There are good linear relationships for the total barrier ΔE, ΔVex and ΔV| with cos3θ respectively, and the same for the dipole moment from PD/LSF model (μPD) and that from ab initio calculation (μQM) vs. cos3θ respectively.