N2 formation in the Lewis-Rayleigh afterglow

Abstract
The nitrogen atom recombination was studied in the slow decaying Lewis-Rayleigh afterglow in a 220 m3 reaction vessel at total pressures between 0.5 and 500 mTorr. The kinetics of formation and depletion of N2(B3Πg) and (a1Πg) were investigated in detail. Molecule formation by preassociation into levels (B3Πg,v′= 13,J′) and (a1Πg,v′= 6,J′ > 13) above the dissociation limit involving 5+ g as intermediary was found. Absolute rate constants of 1.6 × 10–19 and 1.8 × 10–21 cm3 molecule–1 s–1 for the radiative recombination via the transitions N2(B3Πg,v′= 13,J′→A3+ u,v″,J″) and N2(a1Πg,v′= 6,J′ > 13 →X1+ g,vJ″), respectively, were measured. Molecular states B3Πg, v′⩽ 12 below the dissociation limit are populated by collision-induced processes resulting in characteristic primary vibrational distributions dependent on the nature of the third body. Measurements of the three-body recombination in pure nitrogen yielded a rate constant of 2.4 × 10–33 cm6 molecule–2 s–1 for the recombination via the top B3Πg,v′= 9–12 vibrational levels, and a rate constant of about 1 × 10–32 cm6 molecule–2 s–1 for the total chemiluminescence from the B3Πg state. Vibrational relaxation influences the distribution in B3Πg only at pressures above 1 Torr whereas in a1Πg, relaxation is observed above 50 mTorr.