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 functions of indole are computed at the CIS/3-21G and CIS-MP2/3-21 G levels. The (1)L(b) geometry is found to be compatible with experimental vibronic structure. The optimized ground state electronic wave function and energy were obtained using HF and MP2 methods with several basis sets ranging in quality up to MP2/6-31G*. Vertical transition energies, oscillator strengths, and transition dipole vectors were obtained using the STO-3G, 3-21G, 6,31+G, 6-31G*, and 6-31+G* basis sets for the CIS and CIS-MP2 treatments of the excited states. Results are generally similar to those found from INDO/S studies, with higher excited configurations essential for approaching the experimental (1)L(a)-(1)L(b) energy 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 apparent coupling between the diabatic states is quite weak, only about 50 cm(-1)