A PRESSURE-SHIFT STUDY OF ELECTRON-SCATTERING IN DENSE HYDROGEN ARGONGAS-MIXTURES

Rydberg absorption spectra of methyl iodide, CH3I, in hydrogen-argon b inary mixtures of density (2.16-3.14) X 10(20) cm-3 are reported. The Rydberg energy shifts, normalized to a total density of 1 x 10(21) cm- 3, vary linearly with the mole fraction of the binary mixture. Reserva tions concerning this linearity are elaborated. The relationship of sc attering lengths to cross sections for binary scatterers is discussed: cross sections, as obtained from mobility measurements, are additive for binaries whereas, for pressure-shift measurements, it is scatterin g lengths which are additive.