Electron transfer liquid triggered

Figure 3. Time dependence of different electron-transfer trajectories in molecules of pure liquid water at room temperature. The femtosecond UV excitation of water molecules (2X4 eV) triggers either an ultrafast electron photodetachment with the formation of hydronium ions and a nonadiabatic relaxation of excited p-like hydrated electrons (high photochemical channel), or concerted electron-proton transfer (low photochemical channel) (56, 72). The characteristic time of each trajectory is reported on the curve.

We now turn attention to conditions at the electrodes. These play vital roles in establishing the pre-breakdown conditions in the liquid under high electric stress and in triggering the breakdown itself. It has been natural to invoke electron injection at the cathode as an important component since high fields will lower the potential barrier to electron transfer across the interface whether it occurs by a thermally activated or tunnelling process. However, employment of the Schottky formula for field-assisted thermionic emission or the Fowler-Nordheim one for tunnel emission which are appropriately applicable only for electron transfer to a vacuum is a much too simplified solution to the problem. 

The measurement of the photoconductivity of pure liquids or solutions is of fundamental interest since it yields information on the electronic energy levels in liquids. These studies are supplemented by investigations of the radiation-induced conductivity (Chapter 5) and of the charge transfer at interfaces (Chapter 6). From a practical point of view, photo-induced conductivity changes may be applied as laser-triggered fast high voltage switches, photon detectors, or monitors for chemical compounds. 

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