NH2 inversion potential in the S0 and S1 electronic states of aniline: fit to the (ro-)vibrational data and comparison with ab initio and density functional results

An effective one-dimensional Hamiltonian has been determined for the NH2 inversion motion in aniline. The anharmonic potential is represented by a quartic polynomial, fitted to the experimental vibrational transitions in the electronic states S0 and S1. In the S0 state the barrier height is about 580 cm−1 and the equilibrium angle between the NH2 and the ring planes is 44°, while in the S1 state the potential well is extremely flat without a well-defined equilibrium angle. These results are compared with those obtained by ab initio methods. The long-standing discrepancy between the rotational and vibrational results is partially clarified.