Fluorescence and Pre-Ionization in Nitrogen Excited by Vacuum Ultraviolet Radiation

Abstract

Fluorescence in nitrogen following absorption of vacuum ultraviolet radiation has been found to begin at a wavelength of 661.3 Å and to extend to at least 580 Å, the shortest wavelength available in this experiment. The energy of the longest wavelength at which the fluorescence appears is almost exactly equal to the energy required to excite the N2 molecule from the ground state,X 1Σ g +, to the B 2Σ u + state of the N2 + ion. It is thought that the first negative bands of N2 +, B 2Σ u +→X 2Σ g +, are responsible for the observed fluorescence. The fluorescence is excited by dispersed radiation from a stabilized helium gas discharge which produces the Hopfield continuum in the region 580–1100 Å. Fluorescence is also detected in carbon monoxide and in oxygen, but it is too weak for accurate measurements of the appearance wavelength. Experiments with a quartz cell window, in the presence of the electric field from the end window of the photomultiplier, enabled the pre‐ionized bands of nitrogen to be observed.