Photoionization Efficiencies and Cross Sections inO2,N2, CO2, A,H2O,H2, and CH4

Abstract

The photoionization cross sections of several gases were obtained by making simultaneous measurements of the total absorption cross sections and ionization efficiencies in the wavelength region from 473 A to 1100 A. In each case the total absorption cross sections were in agreement with those reported by others. For ${\mathrm{O}}_{2}$, the ionization cross sections were found to be between 5 and 30\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$, while those for ${\mathrm{N}}_{2}$ were close to 23\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$ over almost the entire range studied. The ionization cross section section of argon at the onset of ionization was compared with the theoretical estimate made by Dalgarno. The long-wavelength limits for photoionization were determined and were found to yield ionization potentials in good agreement with those obtained by spectroscopic and electron impact methods.