Quantum study of the internal rotation of methanol in full dimensionality (1+11D): a harmonic adiabatic approximation

The internal rotation of the methanol molecule is studied in full dimensionality i.e., the 12 coordinates are treated explicitly using an adiabatic separation of the 1D-torsional and the 11D-inactive wave functions. The potential energy surface is calculated with the help of quantum chemistry codes and is expanded in a Taylor series up to the second order along the torsional path. Our main results show that the torsional energy levels of this 1+11D-adiabatic model are noticeably different from those of the 1D-models, whether the zero point energy correction along the path is included or not.