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

Abstract

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.