Abstract: The EPR spectrum of 6-methylbenzo [a] pyrene (6-CH3-BaP) in thallium (II1) tris (trifluoroacetate)-trifluoroacetic acid (TTFAJTFA) solutions has been analyzed in terms of the 6-CH3-BaP cation radical with the aid of the ENDOR spectrum. Benzo [a] pyrene (BaP) in TTFA/TFA gives an EPR and ENDOR spectra which are assigned and analyzed as the 6-(tri- fluoroacetoxy) benzo [a] pyrene cation radical. The EPR of several other 6-substituted ...