Radiolysis of Methane in a Wide-Range Radiolysis Source of a Mass Spectrometer. I. Individual and Total Cross Sections for the Production of Positive Ions, Negative Ions, and Free Radicals by Electrons

Abstract

The abundances of, and the total and individual cross sections for, primary products (positive ions, neutral species, and negative ions) resulting from elementary reactions induced by the absorption of energy by CH4 from ionizing radiation (100-eV electrons) have been measured. This was accomplished with the dual electron beam section of our wide-range radiolysis source. The results show that positive ions and free radicals are produced in nearly equal abundances, 45% and 55%, respectively. On the other hand, negative ions are less abundant by about four orders of magnitude. The total cross section for positive ionization (σI) by 100-eV electrons is 3.8×10−16 cm2 and that for the formation of neutral species (σN) is 4.7×10−16 cm2. To independently test the reliability of the dual electron-beam ion source, the total and individual cross sections for ionization of Ar by 100-eV electrons were measured for comparison with published values. Our value for the total cross section (σI) of 3.24× 10−16 cm2 is in satisfactory agreement with those reported by other workers, whose values range from (2.8 to 3.6)×10−16 cm2.