Fluorescence Efficiencies and Collisional Deactivation Rates for N2 and N2+ Bands Excited by Soft X Rays

Abstract

Efficiencies for excitation of the 3914-Å N2+ first negative band and several prominent N2 first positive bands and N2 second positive bands were measured in pure nitrogen and air as a function of gas pressure. These nitrogen bands were excited by the deposition of monochromatic x rays in the energy range 0.9–8.0 keV. The efficiency for the 3914-Å band in air, at pressures where there is no deactivation was determined to be 0.53% ± 0.07%. Efficiency in air was 0.21% ± 0.03% for the 3371-Å N2 second positive band and 0.23% ± 0.08% for the 8912-Å N2 first positive band. The efficiencies of the first negative and second positive bands were invariant for photon energies between 0.9 and 8.0 keV. Quenching of the 3914-Å band in pure nitrogen follows the Stern–Volmer relationship for two-body processes. The quenching constant K was 0.96 torr−1 and the corresponding deactivation rate constant 4.53 × 10−10 cm3/sec. The rate constant for the 3914-Å band, quenched by O2, in air at low pressures, was 7.36 × 10−10 cm3/sec. Three-body processes were evident in air at pressures above 100 torr. The deactivation of the υ′ = 0 vibrational levels in the second positive bands had a rate constant of 1.12 × 10−11 cm3/sec by nitrogen and had a rate constant of 3.12 × 10−10 cm3/sec by oxygen. Quenching constants were measured for seven first positive bands for the sequences υ′ = 1–7. The mean value of K, averaged over all υ′ sequences, was about 3 for nitrogen and 6.5 for air. The deactivation rate constant for the 8912-Å (1, 0) band quenched by N2 was 8.4 × 10−12 cm3/sec.