Photoionization Efficiencies and Cross Sections in ${\mathrm{O}}_2$, ${\mathrm{N}}_2$, C${\mathrm{O}}_2$, A, ${\mathrm{H}}_2$O, ${\mathrm{H}}_2$, and C${\mathrm{H}}_4$

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×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$, while those for ${\mathrm{N}}_2$ were close to 23×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ 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.