Electron transfer cross-beam experiment

One of the main goals of the crossed-beam experiment is to measure the internal energy AEvlh rol transferred to the molecule. In principle, this is possible in either of two ways. First, the scattered molecules could be detected and their product-state population analyzed. Infrared emission or absorption techniques may be considered, similar to those used in cell experiments.13 21 Although such studies would lead to the most detailed results (at least for polar molecules), under crossed-beam conditions they are impossible for intensity reasons, even if the possibility of measuring differential cross sections is renounced and the molecules in the scattering volume itself are detected. Detection via electronic molecular transitions may be invisaged. Unfortunately, the availability of tunable lasers limits this possibility to some exotic molecules such as alkali dimers. The future development of UV lasers could improve the situation. Hyper-Raman... 

Experiments with crossed molecular beams might entail a beam of ferrocene molecules against a beam of chloride ions in the close outer-sphere electron transfer in the gas phase. This should be a very similar process to what we have seen in solution. I d just like to leave the thought that these are two possible directions in which future work will go. 

Two routes have been followed in reaction stereodynamics. One is to orient a molecular reactant in space and see how the reaction cross-section varies with the molecular orientation. This direction has been pioneered in molecular beam experiments using focusing of an electric hexapole field to control the molecular orientation [221-223a]. Numerous studies have applied this technique to electron-transfer reactions of alkaline-earth atoms [223b]. This technique is now complemented by the so-called brute force technique, where polar molecules are oriented in extremely strong electric fields [83]. 

In physical terms, the formation of LiH in the ground state from its constituent atoms occurs by means of a transfer of an electron from the Li atom to H when the internuclear distance decreases below a critical separation R. This same concept underlies the harpoon mechanism which is used to explain the very large cross-sections for reaction which are observed for such processes as K -i- Br2 - KBr + Br. As the reactants approach, the covalent K + Br2 potential surface is intersected by an ionic K Br surface. Accordingly, an electron transfers from K to Br2. Subsequent production of KBr and Br is immediate. This model is also in accord with the observation in beam scattering experiments that the distribution of KBr product is strongly forward-peaked . 

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