Vibration Frequencies and Normal Coordinates of Perylene with Different Molecular Charges A Mindo/3-Forces Treatment

Abstract

AbstractThe MINDO/3-FORCES method was applied for the calculation of the vibration frequencies and normal coordinates of the neutral aromatic perylene molecule and its radical cation and anion. The resulting frequency values were quite near the experimental values when available. Comparison of the results showed that for the C-H and C-C stretching vibrations the sym. mode shows higher frequency values than the asym. As for the CH and CC deformation the asym. vibrations where of higher frequency values than the sym. Comparing the frequencies of the three species with each other it was found that; CH str. (C20H12)˙ + > CH str. (C20H12) >  CH str. (C20H12)˙ ¯ and,sym CC str. > sym CC str.˙ ¯ > sym CC str. ˙ + asym CC str.˙ + > asym CC str. > asym CC str. ˙ ¯ These relations are discussed in terms of the change of the  electron densities at the C atoms of the C-H bonds and the changes in the C-C bond orders of the related bonds.