The Production of Molecular Excited States by Pulsed Electron Beams

Electron pulse radiolysis is a modern, versatile technique for investigating the dynamic properties of physical, chemical and biological change. The technique requires an electron-accelerating machine to produce an intense (0.1-5A) beam of high energy (1-20MeV) electrons in a single pulse (10-9 - 10-5>s). Such a beam, when incident upon a target can create physical and chemical perturbations in sufficient amounts to be directly observed in real time by one of several physical methods. In this work the target liquid occupies the cavity of an optical kinetic spectrometer capable of detecting small changes in light intensity with a resolution of a few nanoseconds. By coupling the output current of the photo-detector to a mini-computer via a fast ADC, and incorporation of sundry digital interfaces, computer control of experimental settings, data acquisition and data-analysis is effected. Using such a device, changes in the nature and concentration of transient species generated during passage of the electron beam through the target medium can be conveniently followed. Molecular excited states are efficiently generated on electron beam bombardment of aromatic liquids such as benzene through direct excitation or fast electron-hole recombination. Both Sl(lB2u) and Tl(3Blu) states are formed which can undergo energy transfer reactions to minor solute components thus populating the respective solute states.