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A wide variety of free radicals can be produced thermally at temperatures as low as 40 degrees C by a new catalytic method which provides a means for studying the mechanism of many catalytic hydrogenation-dehydrogenation processes. Initial results include the first chemical evidence for the existence of the H(3) molecule.

It is now half a century since J. J. Thomson, in 1912, developed the first instrument for measuring mass spectra and discovered two of the isotopes of neon. Following this great work, A. J. Dempster, F. W. Aston, and others constructed several different types of mass spectrometers which were devoted almost entirely to the discovery of new isotopes and to the determination of the relative isotopic abundances and isotopic masses for each of the stable chemical elements. About 1940, the mass spectrometer took on a new function-that of quantitative chemical analysis of hydrocarbons and other gaseous mixtures. Since then the mass spectrometer has been applied to an increasing number of fundamental problems in chemistry and physics. This article is concerned primarily with the development of the mass spectrometer to probe the kinetics and mechanism of various elementary reactions of vital interest to research in the fields of radiation and catalytic chemistry. In the past this type of study has been limited, principally because of the pressure range within which conventional instruments are designed to operate-that is, between 10' and 10-8 millimeter in the reaction chamber. Dr. Martin and Dr. Rummel are on the staff of the chemistry department of Vanderbilt University, Nashville, Tenn. Dr. Melton is a member of the Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn. OCTOBER 1962With the development of a higherpressure mass spectrometer capable of studying reactions up to a pressure of 1 millimeter, the practical feasibility of the mass spectrometer for studying gaseous reactions of ions and other transient species having lifetimes of about 1 microsecond has begun to be recognized. We cite examples of its successful application to a variety of chemical problems in order to demonstrate the immense research potential of this basic and very versatile experimental method. General InstrumentationHigher-pressure mass spectrometers usually have the following general features: (i) maximum detection sensitivity; (ii) a corrosion-resistant ionizing electron filament; (iii) precise control of the energy of the ionizing radiation (electrons, photons, and so on); (iv) differential pumping; and (v) an adaptable ion source assembly.Feature (i), maximum detection sensitivity, is necessary for the general detection of short-lived chemical species such as free radicals and transient ions which are present in minimal concentrations in a given reaction system. The measurement of negative ions is critical, because the production rate is usually 102 to 104 times lower for negative than for positive ions from a given compound under the same operating conditions. Using a 10-to 20-stage electron multiplier as the detector in conjunction with either a pulse counter or an electrometer-recorder read-out device for the mass spectrometer, one can achieve a maximum detection sensitivity of about 1 ion per second, or a 1 0-9-ampere ion beam current.Feature ii, a corrosion-resistant ionizing electron filament, is required to withstand ...