N 2 rotational energy distributions in cold, supersonic beams from electron excited fluorescence measurements of N +2

Abstract

Ground-state rotational energy distributions of N 2 molecules produced in pure and He-seeded supersonic expansions have been determined by measurements of the N + 2 first negative band rotational line intensities produced by 800 eV electron impact on cooled pure and He-seeded N 2 supersonic beams. Sufficient spectral resolution was employed to resolve completely both P and R branches of the first negative bands. Rotational state distributions were obtained to much higher values of J than in previous investigations. The data show that at 800 eV, the electric dipole selection rule, |Δ J| = 1, is consistent with the observed N + 2 emission bands and that the rotational energy distributions produced in the cooled, supersonic beam are non-Boltzmann with a large population in the first few rotational states followed by a long, high-energy fail to quite high J values.