NEW MEASUREMENTS OF FLUORESCENCE EFFICIENCY OF AIR UNDER ELECTRON BOMBARDMENT

The fluorescence efficiency of air under electron bombardment has been measured at a pressure corresponding to an altitude of 65 km, for electron energies around 700 eV, with the principal measurements at the bright 3914-Å band of the N2 + ion. Efficiencies for the 3914-Å band from two methods of observation were in good agreement, and gave a value of η3914 = 0'34 per cent. Spectra were obtained for air emission in the range of 2500-12,000 Å. Comparison of the radiation in the 3914-Å band to that in the whole spectrum gave a total efficiency of ηitT = 1.86 per cent for this spectral range. Efficiencies of other bands were also determined by comparison with the 3914-Å band. The 3914-Å efficiency, for electron energies of from 165 to 1000 eV, was found to be nearly independent of energy. The dependence on pressure of the light output in the spectral range 3000-11,000 Å was observed for electron energies of 750 and 1425 eV and pressures from 30 to 960 μ. The efficiency of the 3914-Å band is independent of pressure below 100 μ. Above 100 μ, efficiencies of the N2 + first negative and the N2 first and second positive bands decrease with increasing pressure, the first positive decreasing most rapidly and the second positive least rapidly. Intensities of some N2 + Meinel bands were compared with the first positive (0, 0) band at pressures from 50 to 1 μ in nitrogen and air. The intensity of the Meinel bands relative to the first positive band increases by an order of magnitude over this pressure range in nitrogen. To check photometric techniques, the cross-section for excitation of the 3914-Å band by 750-eV electrons was measured and found to be in satisfactory agreement with results obtained by Holland. Some electron range measurements also gave results in agreement with previous work. © 1968.