The Quenching of Mercury Resonance Radiation. I. The Effective Cross Sections of Paraffin Hydrocarbons

Abstract

The effective cross sections of the paraffin hydrocarbons from ethane to n-heptane in quenching mercury resonance radiation (λ2537) have been measured by the technique of Zemansky. The effective cross section of ethane is much smaller than the value previously found by Bates. Neopentane is reasonably efficient in quenching λ2537 although it is not decomposed readily by Hg(3P1) atoms. Increase in molecular weight and, up to a point, in branching of the carbon skeleton are accompanied by increases in the effective cross section. The quenching efficiency of the paraffins depends on the number and type of C–H bonds in the molecule and is not primarily a function of the number of carbon atoms or C–C bonds. The effective quenching diameters of the C–H bonds are: primary 0.05 to 0.10A, secondary 0.50 to 0.65A, and tertiary 1.3A; the actual values depending to some extent on the nature of the rest of the molecule. The number of collisions necessary for quenching to occur on primary, secondary, and tertiary C–H bonds is, therefore, approximately 3000, 30, and 5, respectively.