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

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 Dunningʹs 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 2Au(D0)→1 2B3g(D2), 1 2Au(D0)→1 2B1g(D3) and 1 2Au(D0)→2 2B1g(D4) 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 2Au(D0)→1 2B3g(D2) transition are discussed in some detail in the non-empirical fashion.