The mechanisms responsible for the main products in liquid benzene radiolysis (biphenyl, molecular hydrogen, and phenyl radical) are probed with protons, helium ions, and carbon ions of a few to 30 MeV energy. Phenyl. radical yields have been examined using iodine scavenging techniques. The results, are combined with similar data for gamma-rays and suggest that phenyl radicals mainly react with benzene to give a long-lived adduct, which leads to polymer formation. Iodine can react with this adduct to give enhanced yields of biphenyl. Biphenyl is the predominant single hydrocarbon product in the radiolysis of neat benzene with a yield of 0.075 molecule/100 eV. Its yield is nearly independent of radiation type and energy suggesting that its formation in neat benzene is due to a fast ion-molecule process and not due to phenyl radicals. The total yield of 0.7 radicals/100 eV is almost entirely due to phenyl radicals and H atoms. A reexamination of the fluorescence, from the singlet excited state of benzene suggests that this state is the precursor for molecular hydrogen and acetylene, whereas the triplet excited state decays to phenyl radicals and H atoms. Most of the excited states formed in the gamma-radiolysis of benzene seem to decay to ground without formation of any product.