External magnetic field effects on the recombination fluorescence (MARY effect) in the photoionization
reaction of N,N,N′,N′-Tetramethyl-p-phenylenediamine (TMPPD) in water and DMSO/water mixture
are studied. Relatively large magnetic field effects (MFE), ∼ 2–4%, on the fluorescence yield are observed in
the extremely polar water solvent under magnetic fields as small as 3 mT. Such MFE is hardly expected in
water due to instability and very fast escape of the solvated electron from the solvent cage. Enhancement
in the signal-to-noise ratio and superior time resolution characterizing the technique of field modulation
allowed the detection of a very short lived radical ion pair (about 1 ns). The observed MARY spectra illustrate
that the singlet radical ion pair is more reactive than the triplet one.