Aqueous sulfuric acid containing up to similar to 14 M acid (H-0 >= -7.0) was used as solvent in pulse radiolytic redox studies to characterize cationic transients of phenol (C6H5OH) and map their reactions. The primary radical yields were first measured to correlate the variation in various radical concentrations as a function of increasing acid fraction in the solvent. Compared to their respective values at pH 2, the G(Ox(center dot)) increased with almost a linear slope of similar to 0.024 mu mol J(-1) for H-0(-1) (or pH(-1)) up to Ho -6.0 (Ox(center dot) = (OH)-O-center dot + SO4center dot-), whereas G(H-center dot) increased with a slope of -0.033,umol J(-1) for H-0(-1) (or pH(-1)) up to H-0 -5.0. In the presence of > 10 M acid (H-0 < -5.0), phenol was oxidized to its radical cation, C6H5OHcenter dot+, which further reacted with phenol and generated the secondary, dimeric radical cation, (C(6)H(5)oH)(2)(center dot+), following an equilibrium reaction C6H5OHcenter dot+ + C6H5OH reversible arrow (C6H5OH)2(center dot+), with K-eq = 315 +/- 15 M-1. The two cationic radicals were characterized from their individual UV-vis absorption spectra and acidity. The C6H5OHcenter dot+ absorption peaks are centered at 276 and 419 nm, and it was found to be more acidic (pK(a) = -2.75 +/- 0.05) than (C6H5OH)(2)(center dot+) (pK(a) = -1.98 0.02), having its major peak at 410 nm. On the other hand, in the presence of < 6.5 M acid the C6H5O center dot reactions followed the radical dimerization route, independent of the parent phenol concentration.