Franck-Condon effects in low-energy states of C10H8+ radical.: Ab initio MCSCF study of absorption and resonance Raman spectra

The Franck-Condon (FC) effects in the low-energy states of the C10H8+ radical are investigated in terms of ab initio FORS (full optimized reaction space) and SDE (single and double excitations) MCSCF calculational scheme applied with Dunning's double-zeta (DZV) basis set. This scheme is used to determine the excitation energies, the transition dipole moments and displacement (Franck-Condon) parameters for the three low-energy dipole-allowed 1 (2)A(u)(D-0) --> 1 B-2(3g)(D-2), 1 (2)A(u)(D-0) --> 1 B-2(1g)(D-3) and 1 (2)A(u)(D-0) --> 2 B-2(1g)(D-4) transitions. The results of FORS MCSCF computations are compared to the QCFF/PI + CI and ROHF/3-21G results reported most recently for the C10H8+ radical. The resonance Raman (RR) spectra available in the region corresponding to the lowest-energy dipole-allowed 1 (2)A(u)(D-0) --> 1 B-2(3g)(D-2) transition are discussed in some detail in the non-empirical fashion. (C) 1998 Elsevier Science B.V. All rights reserved.