A scheme for the specific mass-spectrometer detection of radicals

Abstract

In most environments in which radicals occur, the precursor molecule is found in much higher concentrations than that of the radical. Mass-spectrometer detection of radicals is then essentially impossible because the mass-spectrometric signature of a radical is nearly identical to that of the parent. A new method for overcoming this difficulty has been demonstrated. This scheme is based upon the means by which radicals were first detected and involves the propensity for radicals to react with tellurium to produce volatile tellurides. A mass spectrometer can detect the tellurides thus produced in a region of the mass spectrum far removed from that of the radical’s precursor. This technique has been used in analyses for CH₃, CF₃, CF₂H, CFH₃, C₂F₅, and F at partial pressures as low as 2 × 10^–8 Torr in the presence of the parent hydrofluorocarbons at five orders of magnitude greater pressures. Possible interferences by the neutral precursor, by ions, and by the products of reactions on the tellurium surface have been investigated.