High-Resolution Electron Energy Loss Spectroscopy: Absolute Cross Section Measurements for Low Energy Electron Scattering from Biomolecules

Abstract

Low-energy electron (LEE) scattering by molecules is a topic of importance in many areas, such as astrochemistry, plasma science, nanolithography, fast-laser photochemistry and the radiobiological sciences. In the latter field, the passage of high-energy particles or photons in biological matter produces copious amounts of LEEs. These latter are highly reactive and interact within biological media via inelastic collisions that ionize and excite vibrationally and electronically biomolecules. They can additionally attach temporarily to biomolecules to form transient anion states that modulate and enhance excitation and dissociation cross sections (CSs). Since LEEs are one of the most abundant immediate species formed following irradiation, it is necessary to comprehend and model their interactions within biological media. Radiobiological models often rely on Monte Carlo (MC) simulations that can describe event-by-event modifications of the biological medium, predict the number of secondary species created and calculate the deposited energy after the passage of ionizing radiation. These MC and track-structure calculations require a large number of parameters and values that are related to interaction probabilities, including CSs for LEEs scattering from biomolecules. Preferably, these CSs should be obtained in the condensed phase, for such calculations to produce data closer to cellular conditions. In this chapter, we explain the use of high-resolution electron energy loss spectroscopy (HREELS), as a powerful experimental technique to study and measure absolute CSs for LEEs scattering from condensed molecules. We review absolute CSs from the literature, which were derived from this technique with biologically relevant molecules, including those of the basic DNA constituents.