Vibration Frequencies of Perylene with Different Molecular Charges

The (B3LYP) Density Functional Theory (DFT) method was applied for calculating thevibration frequencies and normal coordinates of the neutral aromatic perylene molecule as wellas its radical cation and anion. Comparison of the results showed that for the C-H stretchingvibrations, the symmetric mode shows higher frequency values than its correspondingasymmetric. As for the C-C stretch, as well as the δCH and δCC deformation vibrations theasymmetric vibrations were of higher frequencies than the symmetric one. Comparing thefrequencies of the three differently charged species with each other, it was found that;νCH str. ·+ νCH str. ^° νCH str. ^·- and, νsym ^CC str. νsym ^CC str. ^˙+ νsym ^CC str.˙ ¯ for some modes; and; νsym ^CC str.^+ νsym ^CC str. νsym ^CC str.·¯ for other modes. These relations are discussed in terms of the change in the σ electron densities at the H atoms of the C-H bonds and the changes in the bond orders of the related C-C bonds.