Free Radical Beam Source

Abstract

A source of pure beams of thermal alkyl radicals for molecular beam scattering experiments is described. A parent compound, (CH₃)₂Hg, (CH₃)₃Bi, CH₃I, or (C₂H₅)₂Hg, was pyrolyzed in an array of small Ta tubes, and a beam of the products entered a slotted disk type velocity selector. Selection at 1500 m/sec chemically purified the radical beam by removing parent molecules and high mass decomposition products. The best purities, found by modulated beam mass spectrometry, average to 94±8 mole% CH₃, and in these runs the estimated intensities were 2−7×10¹⁵ radicals/sr·sec, or 3−10×10¹³ radicals/cm²·sec at the detector. Light hydrocarbons (C₁,C₂) were the major impurities, their concentration increasing with methyl flux.