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(B³Π_g) and (a¹Π_g) were investigated in detail.

Molecule formation by preassociation into levels (B³Π_g,v′= 13,J′) and (a¹Π_g,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(B³Π_g,v′= 13,J′→A³∑⁺_u,v″,J″) and N₂(a¹Π_g,v′= 6,J′ > 13 →X¹∑⁺_g,v″J″), respectively, were measured.

Molecular states B³Π_g, 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 B³Π_g,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 B³Π_g state.

Vibrational relaxation influences the distribution in B³Π_g only at pressures above 1 Torr whereas in a¹Π_g, relaxation is observed above 50 mTorr.