ULTRA-FAST EVENTS IN RADIATION-CHEMISTRY

Secondary electrons, produced in a large number by ionizing radiation, deposit their energy via specific processes which usually occur within the sub-picosecond time domain. Those ultra-fast processes occurring in condensed materials, which were investigated with low-energy electron beam methods are reviewed in the present article. They include elastic scattering, vibrational and electronic excitation, dissociative ionization and dissociative attachment. The existence of ultra-fast reactions (10(-14)-10(-13) s) involving products formed by secondary electrons is demonstrated. It is also shown that transient negative ion formation (i.e., electron resonances) is an important and usually dominant mechanism in the process of energy losses by secondary electrons with energies below 20 eV. In this energy range, elastic scattering depends on the band structure and the geometrical arrangement of the constituents of condensed matter.