Interaction of 25 keV Electrons with the Nucleic Acid Bases, Adenine, Thymine, and Uracil. I. Outer Shell Excitation

The energy loss functions — Im(1/ε) of thin films of the nucleic acid bases, adenine (C5N5H5), thymine (C5N2O2H6), and uracil (C4N2O2H4) have been determined in the range 2–50 eV from energy loss experiments with 25 keV electrons at room temperature. An analysis of the electronic structure of these materials in the region of outer shell excitation has been obtained in the form of determination of the dielectric constants ε1 and ε2 from a Kramers—Kronig analysis of the energy loss function. In the spectral region where ultraviolet absorption data exists (<10 eV), the calculated optical absorption coefficient μ is shown to be in good agreement with the optical measurements.