X-Ray Radiolysis of Condensed Systems: Solid DNA and DNA Solutions
We have seen in the previous lectures that the effect of ionizing electromagnetic radiation on a system is, at the first stage, the production of high energy electrons by photoelectric or Compton effect. The fast moving electrons transfer their energy to the molecules of the system in the vicinity of their trajectory by ionization or excitation processes. These primary products, excited molecules, positive ions and ejected electrons undergo secondary reactions which ultimately lead to stable products. The yields of primary ionization and excitation depend on molecular properties that are at the present largely unknown. The most important of these properties is the excitation spectrum, which we have seen is closely related to the absorption spectrum of the molecule extending from the visible region to the X-ray region. The synchrotron radiation has been used for experiments in this field(1,2). The absorption spectroscopy and the experimental set up for experiment using synchrotron radiation are topics of other lectures so we will simply show, as an example, the result obtained on benzene, in the region up to 35 eV (figure 1)(2). The upper spectrum is a generalized excitation spectrum with the three regions of excitation, super-excitation and ionization, the bottom one is the absorption spectrum of benzene. This spectrum covers the whole interesting region, the one of superexcited state formation.
KeywordsSynchrotron Radiation Primary Ionization Pulse Radiolysis Transient Absorption Spectrum Compton Effect
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