Photo-Ionization of N₂ in the 734–805 å Region

Absolute photo-ionization coefficients and ionization efficiencies of N 2 have been measured in the 734–805 Å region using a 1-meter Seya–Namioka scanning vacuum monochromator with the Hopfield helium continuum as a background light source.The ion-current spectrum obtained has been compared with the absorption spectrum observed photographically. Nearly all of the absorption bands with higher energies than the first ionization potential showed ion-current peaks, indicating pre-ionization. However, their ionization efficiencies showed strong fluctuations whose magnitudes decreased toward the shorter wavelengths. The spectral regions with the lowest absorption coefficients (180–340 cm −1 ) beyond the first ionization potential showed the highest efficiencies, the values of which were about 80%. Efficiencies of bands with m[Formula: see text] of the Ogawa–Tanaka Rydberg series were much larger than those of the corresponding bands of the Worley third Rydberg series. The progressions (1) and (2) had a rather high efficiency of 70% which increased slightly with an increase of the vibrational quantum numbers of the upper electronic states.