MCSCF Study of the Structure and Vibrational Frequencies of the Lowest Excited Singlet State of Benzene

Abstract

The molecular structure and vibrational frequencies are evaluated for the ground and the lowest excited singlet states of benzene by using ab initio MCSCF method. In the calculation, STO-3 G basis set is used, and all the electron configurations in six π orbitals are considered in the MCSCF procedure. The result shows that benzene in ¹B_2u state has D_6h symmetry, and C-C and C-H bond lengths are calculated to be 1.4498Å and 1.0818Å, respectively. The O-O transition energy is determined to be 4.727 eV. The ordering of the vibrational frequencies agrees very well with experimental results. The normal vibrational vectors obtained from the present theoretical calculation would help to refine the empirical force field, especially on b_2u and e_1u modes.