Fluorescence Efficiencies of Nitrogen Excited by 1–5-MeV Positive Ions

Fluorescence efficiencies for excitation of nitrogen by 1–5-MeV positive ions have been measured at pressures of 2–19 torr. Typically, N2 pressure of 3.6 torr was required to stop a beam of 4-MeV Ne+ in the 1.5-m-long collision chamber. Power output in the 3914-Å (0, 0) N2+ first negative band was measured with a photometer, and low-pressure efficiencies were calculated from the collisional deactivation rate. For Ne+, O+, N+, N2+, and O2+ ions with various initial velocities from 3.1 to 8.3 × 108 cm/sec, the low-pressure efficiencies were between 0.4% and 0.6%. 3914-Å efficiencies were, for 2.0 and 3.4 × 108 cm/sec Kr+, 0.27% and 0.35%, and for 1.38 × 109 cm/sec H+, 0.67%. Spectra of the nitrogen emission in the 3400-7800-Å range were recorded. N2+ first negative and N2 first and second positive bands were prominent, with most first negative in the υ′ = 0 vibrational sequence, and most second positive in the υ′ = 0 − 2 sequences. The spectra were corrected for collisional quenching and low-pressure efficiencies were determined relative to the 3914-Å band. For 4–5-MeV, N+, Ne+, N2+, and Kr+, total efficiencies for the second positive υ′ = 0 − 2 sequences were about 1.5 times the 3914-Å efficiencies. Efficiencies were determined for 10 first positive bands of the υ′ = 2 to 7 sequences excited by 4.75-MeV Ne+; the (2, 0) and (3, 1) band efficiencies, for example, were about one-fourth the 3914-Å efficiency of 0.52%. The nitrogen fluorescence excited by the ions has a spectral intensity distribution similar to those observed by Hartman for 850-eV electrons in air and by Mitchell for 1.5-keV x rays in N2.