The Study of Reaction Intermediates by Means of a Mass Spectrometer Part I. Apparatus and Method

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Abstract
A method for coupling a reaction chamber to a Dempster‐type mass spectrometer in such a manner that short lived intermediates can reach the electron beam is described. The presence of radicals is denoted by an increase in the ion current of the corresponding mass. The sensitivity of the method depends on the difference between the appearance potential of the given ion produced by electron bombardment of either reactants or end products and the ionization potential of the free radical. It is shown experimentally that excited molecules are not present in sufficient quantity to invalidate the assumption that free radicals are responsible for the changes in ion current. The method has already extended more than tenfold the pressure range in which radicals are detectable, thus bridging the gap between mirror and spectroscopic methods so that low pressure combustion phenomena may be studied.