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Measurement of inelastic cross sections for low-energy electron scattering from DNA bases

Abstract Purpose: To determine experimentally the absolute cross sections (CS) to deposit various amount of energies into DNA bases by low-energy electron (LEE) impact. Materials and methods: Electron energy loss (EEL) spectra of DNA bases were recorded for different LEE impact energies on the molecules deposited at very low coverage on an inert argon (Ar) substrate. Following their normalisation to the effective incident electron current and molecular surface number density, the EEL spectra were then fitted with multiple Gaussian functions in order to delimit the various excitation energy regions. The CS to excite a molecule into its various excitation modes were finally obtained from computing the area under the corresponding Gaussians. Results: The EEL spectra and absolute CS for the electronic excitations of pyrimidine and the DNA bases thymine, adenine, and cytosine by electron impacts below 18 eV were reported for the molecules deposited at about monolayer coverage on a solid Ar substrate. Conclusions: The CS for electronic excitations of DNA bases by LEE impact were found to lie within the 10216 to 10218 cm2 range. The large value of the total ionisation CS indicated that ionisation of DNA bases by LEE is an important dissipative process via which ionising radiation degrades and is absorbed in DNA.