Photoionization Cross Section of Nitric Oxide

The photoionization cross section of the NO molecule was measured in the spectral region 1070-1343A, at intervals of one to five angstroms, using a vacuum monochromator (band width 0.85A), an absorption cell with ion collector, and a detector calibrated against a thermocouple. The ionization continuum showed some structure which was ascribed partly to preionization of several bands in the region 1070-1150A and partly to vibrational levels of the ground state of NO⁺ ion. The photoionization cross section at Lyman alpha was 1.24×{}10^-18 cm², about one-half the total absorption cross section. The first ionization potential, 9.23±{}0.02 ev, was obtained from the long wavelength limit of the ionization continuum. Application of the method to other molecules appears promising.