Summary
Two different e.p.r. spectra have been observed after bombardment of dry powders of thymine and thymidine with discharge-excited helium, argon and nitrogen: the characteristic eight-line spectrum due to the C6-adduct of atomic hydrogen to the base and a singlet interpreted as being formed by dissociation of the thymine C6-H bond. The hydrogen atoms generated in this way are responsible for the adduct formation.