Ab initio study of the structure of aniline in the S1 and S2 ππ states

Ab initio calculations at the CIS level of theory combined with several basis sets were performed to elucidate the geometry of the two lowest pi pi* singlet states of aniline. A global picture emerges from this study. The 6-31 + + G* basis set was the only one to give convergence for the S-1 and S-2 states while, for example, the CIS/6-31G* results refer to the S-2 state and the S, optimization does not converge. Aniline in the S, state is quinoidal; in the S2 state the ring expands relative to the ground state. Planar geometry is predicted for both states. (c) 2005 Elsevier B.V. All rights reserved.