Thermal Methods for Detection of Free Radicals

Thermal Methods for Detection of Free Radicals. The recombination of radicals and atoms liberates a considerable quantity of heat, one that is at least equal to the energy of the bond formed. Since, at low pressures, it has been found that recombination of radicals takes place heterogeneously, i.e., at surfaces, it is possible to measure the relative concentrations of radicals by measuring the heat liberated when they recombine on a surface. 

The thermal element used may be a coated thermometer bulb, a glowing wire, or a thermocouple junction.  

The method requires careful calibration and a study of possible poisoning of the metal surface. It can, however, be used quite generally for all types of radicals and atoms. The atoms may be produced by the methods already discussed or by electrical excitation. One of the most useful devices 

The tube was first used by Wood and later modified by Bonhoeffer. In operation, a fast stream of low-pressure H2 (with or without carrier gas such as He or Ne) is drawn past a 3000- to 5000-volt discharge (up to 

300 ma). Water, KCl, or syrupy H3PO4 may be used to poison the walls and prevent recombination of H atoms. The pressures are from 0.1 to 

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