Vibration Frequencies Shifts of Naphthalene and Anthracene as Caused by Different Molecular Charges

Abstract

Semi-empirical SCF-MO calculations were carried out for the naphthalene and anthracene radical cations and anions. For all ions D2h symmetry was obtained. All 3N-6 vibration frequencies for all species were calculated and assigned, applying the Herzberg convention. The valence assignment of the vibration modes was possible applying graphical pictures of each mode and the so called atomic partial participation (APP) values. Interesting relations between the frequencies of the ions were obtained, e. g. for the radical cation of naphthalene νsym(CHβ str.) ·+ > νasym(CHβ str.)·+ > νsym(CHα str.)·+ > νasym(CHα str.)·+, and for its anion νsym(CHα str.)·− > νasym(CHα str.)·− > νsym(CHβ str.)·− > νasym(CHβ str.)·−, as well as for both ions νsym ring (Cβ-Cβ ) str. > νasym ring Cα-Cβ) str. > νsym ring (C9-C10) str. Similar correlations were detected for the anthracene ions. Interionic correlations could be observed for the frequencies of similar modes for the ions and neutral molecules, e. g. for naphthalene νsym(CHβ str.)·+ >νsym(CHβ str.) >νsym (CHβ str.)·− and νsym(CHα str.)·+ >νsym(CHα str.) >νsym(CHα str.)·−. Generally the calculated frequencies for the radical anions were nearer to those of the neutral molecule than those of the radical cations.