Calculation of the normal vibrations of benzene in the first singlet electron-excited state 1B2u

Using the CIS/6-311+G** method, the normal vibrations of the benzene molecule in the first singlet electron-excited state 1B 2u have been calculated. The algorithm of calculation of the force field in dependent coordinates by the method of generalized inversion is described. A method of autoscaling in dependent natural coordinates is suggested. For six groups of natural coordinates scaling factors have been obtained, the use of which has led to agreement between the calculated and experimental frequencies of the vibrations of benzene. The frequencies of the B1u-symmetry-type vibrations, for which there is no experimental assignment, have been calculated. The problem of selection of the force field in dependent coordinates is discussed.