Photoionization and Total Absorption Cross Section of Gases. I. Ionization Potentials of Several Molecules. Cross Sections of NH3 and NO

Ionization potentials determined by examining the long wavelength limit of the ionization continuum for H2S, CS2, C6H6, toluene, p-xylene, C2H4, butadiene, and CH3I agreed with spectroscopic values obtained by Price and co-workers. Values are reported also for NH3, NO, acetone, methyl-ethyl-ketone, CH3OH, and C2H5OH. Improved energy measurements showed that photoionization cross sections of NO in the region 1070—1340A obtained earlier were about 40 percent too low. At 1215.6A the photoionization and the total cross sections are 2.0×10—18 and 2.4×10—18 cm2, respectively, the difference being ascribed to an absorption band. The photoionization cross section of NH3 was found to rise rather gradually with decreasing wavelength in the region 1220—1060A and to reach a value of 9×10—18 cm2 at 1060A.