Electrically excited halogen atoms

These experiments show conclusively that the available energy is released almost entirely as internal excitation of the products. The observation that the diatomic product can subsequently excite M atoms electronically demands a degree of excitation which precludes the formation of 2P1/2 halogen atoms, which requires 21.7 kcal/mole (0.94 eV) for I and 10.5 kcal/mole (0.46 eV) for Br. Where electric deflection analysis has been performed [34-36], the averaged rotational energy yield, is about 5 kcal/mole (0.22 eV),... 

Quite recently, a class of excimer lasers has been discovered which are pumped by chemical reactions between halogen molecules and excited metastable rare gas atoms. Although these new excimer systems are dependent upon electrical excitation for creation of the metastable atoms and therefore cannot be classified as purely chemical, they nevertheless demonstrate that very high laser-pulse energies at ultraviolet wavelengths can be achieved through chemical reaction. It is safe to predict that excimer systems... 

When an electric discharge is passed through a cold diatomic gas at low pressure it is partially dissociated into atoms in this way reasonable concentrations of O, H, D, N, halogen or other atoms can be produced in a chemically inert diluent. The recombination of these atoms, and their reaction with other molecules can be observed as the gas flows down a long tube. Many of the reactions produce molecules in excited electronic states the resulting chemiluminescence can be used to measure the concentration of atomic species as a function of distance, and hence time, down the tube. Dr Clyne describes this important technique, which has produced direct measurements of the rates of many exothermic reactions of atoms and free radicals at room temperature and below. The reverse of the recombination steps are, of course, the dissociation reactions whose kinetics at high temperatures were described in the first chapter if the ratio of forward and reverse rate constants is equal to the equilibrium constant, the temperature dependence of these rates can be deduced over very wide ranges of temperature. 

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