Infrared spectroscopy for wavenumbers ranging from 10,000 to$300\ {\rm cm}^{-1}$ is used to study the action of ionizing radiation (0.8 MeV electrons) and nonionizing ultraviolet light (Hg lamp 2537 Å) on thin solid film samples of purines, pyrimidines, and their derivatives. Our data indicate that of all the bases studied only pure uracil is highly resistant to electron irradiation, whereas all the other bases and their derivatives including uracil derivatives damage readily. Damage is exhibited by bond breaking manifested by decreases in intensity of various absorption peaks, or by the appearance of new absorption peaks indicative of new groups. Intense new absorption peaks in the region of$1100-1400\ {\rm cm}^{-1}$ appear in thymine, uracil, 1-methyl thymine, and deuterated thymine and uracil subsequent to uv irradiation. Low temperature spectra have been taken and inert atmosphere uv irradiations have been tried using thymine. There are distinct differences between irradiation effects of uv light and 0.8 MeV electrons indicating selectivity of damage sites at various parts of the biomolecules.

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