A theoretical study of the B-1(2u) and B-1(1u) vibronic bands in benzene

Citation
A. Bernhardsson et al., A theoretical study of the B-1(2u) and B-1(1u) vibronic bands in benzene, J CHEM PHYS, 112(6), 2000, pp. 2798-2809
Citations number
51
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF CHEMICAL PHYSICS
ISSN journal
00219606 → ACNP
Volume
112
Issue
6
Year of publication
2000
Pages
2798 - 2809
Database
ISI
SICI code
0021-9606(20000208)112:6<2798:ATSOTB>2.0.ZU;2-K
Abstract
The two lowest bands, B-1(2u) and B-1(1u), of the electronic spectrum of th e benzene molecule have been studied theoretically using a new method to co mpute vibronic excitation energies and intensities. The complete active spa ce (CAS) self-contained field (SCF) method (with six active pi-orbitals) wa s used to compute harmonic force field for the ground state and the B-1(2u) and B-1(1u) electronic states. A linear approximation has been used for th e transition dipole as a function of the nuclear displacement coordinates. Derivatives of the transition dipole were computed using a variant of the C ASSCF state interaction method. Multiconfigurational second-order perturbat ion theory (CASPT2) was used to obtain absolute excitation energies (12 act ive pi-orbitals). The results show that the approach works well. Vibrationa l progressions are well described in both bands and intensities, and energi es are in agreement with experiment, in particular when CASPT2 derived geom etries are used. One interesting result is that computed vertical energies fall about 0.1 eV on the high energy side of the band maximum. (C) 2000 Ame rican Institute of Physics. [S0021-9606(00)30306-3].