Resonance raman spectra of würster's cation dimers: p-phenylenediamine and 2,3,5,6-tetramethyl-p-phenylenediamine

Resonance Raman spectra have been observed for the dimers of p -phenylenediamine cation (PPD + ) and of 2,3,5,6-tetramethyl- p -phenylenediamine cation (TMPD + ). When the exciting light frequency approached the absorption bands characteristic of the dimers, new polarized Raman lines appeared at 161 cm −1 for (PPD + ) 2 and at 117 cm −1 for (TMPD + ) 2 with a striking resonance enhancement. The resonant behaviour as well as the frequency values indicate that they are reasonably assigned to the interradical stretching vibrations of the parallel D 2h dimer molecules.