Cross sections for low energy (1-12 eV) inelastic electron scattering from condensed thymine

摘要

We describe a new method to obtain the absolute integral cross sections per scatterer for inelastic electron scattering from sub- and monolayer film of molecules condensed on an inert surface. These cross sections are determined by means of a high-resolution electron-energy loss (HREEL) spectrometer for electrons of incident energies similar to those of secondary electrons generated by high energy radiation, i.e. 1-12 eV. Using the linear relationship between the reflected and transmitted current, a HREEL spectrum can be normalized in such a way that the energy integral performed over an energy loss feature can be expressed in terms of an absolute reflectivity value. Given the thickness of the film and assuming thin film and single collision conditions, those reflectivity values can then be converted into absolute integral cross sections for inelastic electron scattering. As an example, we report the energy dependence of the cross sections for the vibrational excitations of thymine. The maximum of 1.6 x 10~(16) cm~2 at about 4 eV in the cross section for an energy loss of 95 meV is attributed to the formation of a transient anion state that is decaying into vibrational excitation channels.