The dominant features in the transient absorption spectra of 6-methylpurine (P) in aqueous solution, following laser excitation at 266 nm, are the triplet-triplet and the hydrated electron (e(aq)) absorption bands. Upon applying a weak magnetic field (H) of 234 G, the ionization yield increases 200%, whereas the population of triplet molecules remains the same, indicating that P is not ionized from the triplet manifold. Electronically excited P(S-1) is the precursor of a geminate radical cation-electron pair (1){P.+, e}, that evolves into an intermediate with triplet multiplicity (3){P.+, e} that is sensitive to H and from which e(aq) is produced. (C) 2003 Elsevier B.V. All rights reserved.