PHOTOIONIZATION MECHANISM OF ANILINE DERIVATIVES IN AQUEOUS-SOLUTION STUDIED BY LASER FLASH-PHOTOLYSIS

The photoionization mechanism of a series of aniline derivatives in aq ueous solution was investigated by 266 or 308 nm laser flash photolysi s to determine the molecular properties which pray an important role i n the photoionization of solute molecules in aqueous medium. The ioniz ation potentials of the investigated compounds in the gas phase (IPgas ) are in the range 6.87-8.64 eV. In compounds with IPgas values of les s than approximately 7.8 eV, photoelectron ejection takes place mainly from the non-relaxed S-1 state by one-photon absorption at 266 nm (4. 66 eV) or 308 nm (4.03 eV), showing that significant polarization stab ilization of the cation as well as of the photoejected electron should occur in aqueous solution. Contrary to expectation, the hydrated elec tron yield (Phi(<e(aq)over bar>)) determined from transient absorption measurements tends to increase with increasing IPgas. The Phi(<e(aq)o ver bar>) value increases with increasing positive charge (i.e. formal charge) on the nitrogen atom of the resulting cations, indicating tha t the interaction between the local positive charge on the cation and the solvent water molecules is one of the key factors in the photoioni zation of aqueous aniline derivatives. (C) 1997 Elsevier Science S.A.