The electronic structure of aqueous p-aminophenoxyl radical (H2NPhO.) has been examined by time-resolved resonance Raman spectroscopy and ab initio and density functional theories. The effects of hydrogen bonding and solvent reaction field on polarity of the radical have been visualized in terms of simple models. Calculations predict the dipole moment of the radical in its ground electronic state (B-2(1)) to increase by 8(+/-2) D and the difference between the CN and CO bond lengths to decrease by similar to0.05 Angstrom from gas phase to aqueous solution. This profound hydration effect converts the structure and chemical properties of H2NPhO. from a substituted phenoxyl radical in the gas phase to a semiquinone-like radical in water. The observation of vibrational modes enhanced in Raman by a non-Franck-Condon vibronic coupling mechanism has led to the identification of two very weakly absorbing electronic states of (2)A(2) symmetry in the 340-390 nm region, which borrow transition moment from close by strongly allowed electronic states of B-2(1) symmetry at lower (similar to440 nm) and higher (similar to320 nm) energies. One of these transitions is parity forbidden (B-2(2g)<->B-2(1g)) in p-benzosemiquinone radical anion (PhO2-.) and p-phenylenediamine radical cation (Ph(NH2)(2)(+.)) and this is the first experimental evidence on energy location (3.44 eV) of this transition in an isoelectronic radical. The experiment and theory are combined to estimate the CO and CN bond lengths in H2NPhO. as similar to1.263 and similar to1.34 Angstrom, respectively, in liquid water and similar to1.245 and similar to1.37 Angstrom in the gas phase. (C) 2003 American Institute of Physics.