m-Tolunitrile–H2O complex: Isomers and methyl torsional potentials analyzed by the time-dependent density-functional theory

Density-functional theory (DFT) and time-dependent DFT (TD-DFT) were employed to calculate methyl torsional potentials of the m-tolunitrile monomer and two isomers of m-tolunitrile–H2O complex. Geometries in their ground electronic states (S0) were optimized at fixed torsional angles of 10-degree intervals with DFT. Torsional potentials in their first excited singlet electronic states (S1) were obtained by calculating vertical excitation energy with TD-DFT for each optimized geometry in S0. By comparing torsional potentials obtained by the calculations with those determined by analyzing observed torsional frequencies, we could determine the geometries of two isomers of m-tolunitrile–H2O complex that had been observed spectroscopically.