Packing Fractions of Krypton and Xenon

Abstract

THE lines produced in mass spectra by hydrocarbon molecules have always played a predominant part in the accurate measurements of mass. This is particularly so in the use of the doublet method, since their high masses, due to the hydrogen, tend to provide easily resolvable doublets with ordinary atomic lines. With methane and ethane there is no difficulty in producing all the lines of the C₁ and C₂ groups, but when propane is used in a cylindrical discharge tube, only the first four lines of the C₃ group, 36, 37, 38 and 39, have a workable intensity. These were used in the measurements of the isotopes of chlorine¹. Fortunately, the lower pressure discharge in an eight-inch bulb gives all the lines up to C₃H₈, though the even ones, 40, 42, 44, are weaker than the others. This has enabled comparisons to be made with the multiply charged lines of krypton and xenon, giving direct measurements of their packing fractions much more accurate than the indirect ones made ten years ago². The following are the results: