INFLUENCE OF MEDIUM VISCOSITY ON THE EFFE CT OF MAGNETIC-FIELD IN THECHLOROPHYLL-A OXIDATION REACTION

The effect of a magnetic field on the yield of chlorophyll cation radi cals upon steady-state excitation of a system chlorophyll a - parabenz oquinone in ethanol was studied. The viscosity of the solvent was chan ged by glycerine addition. It was shown that [Chl(+)...Q(-)] radical p airs are first formed as triplets, and the application of an external magnetic field leads to an increased yield of chlorophyll cation radic als. The relative effect of the magnetic field on the yield of Chl(+), R(B), and the B-1/2 value depend on the viscosity of the solvent and increase monotonically as eta increases from 1,2 to 900 sP. It is assu med that the increase in B-1/2 is due to the following reasons: (1) as eta increases, the value of B1/2 depends not only on the time the [Ch l+..Q-] radical pair stays in the cell but also on the time of transve rse spin relaxation in the pair; (2) the efficiencies of formation and dissociation of [Chl(+)..Q(-)] pairs change differently with increasi ng eta. A correlation between the dependences of the intensity of diff erential absorption spectrum for Chl(+), which was registered by magne tooptical differential spectroscopy, and the R(B) value on viscosity o f the solvent was found.