Ab initio MO and quasi-classical direct ab initio MD studies on the nitrogen inversion of trimethylamine

A coupled motion of the skeletal inversion and methyl torsion in trimethylamine is investigated theoretically at various levels up to MP4(SDQ)/aug-cc-pVTZ. Among possible structures, the pyramidal C3v is the only minimum energy structure, and the planar Cs is the transition state structure of the nitrogen inversion. Our best estimate of the barrier height (without zero-point energy) is 3290 cm−1. The quasi-classical direct ab initio MD using HF/6-31G* starting from the pyramidal C3v structure indicates that the coupled methyl torsional motion is the primary factor for the nitrogen inversion of trimethylamine.