MOLECULAR-ORBITAL THEORY OF THE (1)L(A) AND (1)L(B) STATES OF INDOLE .2. AN AB-INITIO STUDY

The (1)L(a) and (1)L(b) excited state optimized energies and wave func tions of indole are computed at the CIS/3-21G and CIS-MP2/3-21 G level s. The (1)L(b) geometry is found to be compatible with experimental vi bronic structure. The optimized ground state electronic wave function and energy were obtained using HF and MP2 methods with several basis s ets ranging in quality up to MP2/6-31G. Vertical transition energies, oscillator strengths, and transition dipole vectors were obtained usi ng the STO-3G, 3-21G, 6,31+G, 6-31G, and 6-31+G* basis sets for the C IS and CIS-MP2 treatments of the excited states. Results are generally similar to those found from INDO/S studies, with higher excited confi gurations essential for approaching the experimental (1)L(a)-(1)L(b) e nergy gap. The two energy surfaces exhibit an avoided crossing as the geometry is varied between the (1)L(b) and (1)L(a) minima. The apparen t coupling between the diabatic states is quite weak, only about 50 cm (-1)