Time-resolved resonance Raman spectroscopy of p-aminophenol radical cation in aqueous solution

Examination of the intermediates associated with the 410-450-nm absorption in the pulse radiolytic oxidation of aqueous p-aminophenol by time-resolved resonance Raman spectroscopy shows that below pH 2 the transient species responsible is the p-aminophenol radical cation. Strongly resonance enhanced in the Raman spectrum of the radical cation are the {nu}{sub 8a} phenyl ring stretching vibration at 1,631 cm{sup {minus}1} and the {nu}{sub 9a} CH bending vibration at 1,178 cm{sup {minus}1}. The phenyl modes {nu}{sub 7a} and {nu}{sub 13}, which involve significant contributions from the CN and CO stretching motions, are observed prominently at 1516 and 1406 cm{sup {minus}1}. In basic solutions this absorption spectrum, which is shifted slightly to the red, is ascribed to the p-aminophenoxyl radical. In the neutral radical the CN and CO stretching motions are strongly coupled, and only one intense band representing the in-phase vibration is observed at 1,434 cm{sup {minus}1}.