A 3Σ+u molecules in the N2 afterglow

Abstract

Excitation of N₂ by electrons with energy below the ionization threshold produces a strong afterglow in the B ³Π_g–A ³Σ⁺_u system. The precursor is identified as the A ³Σ⁺_u state in the v≳6 vibrational levels. The peak electron cross section of the A ³Σ⁺_u–X ¹Σ⁺_g system is estimated at about three times the B ³Π_g–X ¹Σ⁺_g transition. Deactivation rates of the A ³Σ⁺_u v≳6 levels by X ¹Σ⁺_g molecules vary over the 8E−12 cm³sec⁻¹–5E−11 cm³sec⁻¹ range. There is some evidence that the higher levels may relax at rates comparable to that of electronic deactivation. Deactivation of B ³Π_g by X ¹Σ⁺_g molecules has a strong dependence on the vibrational level of the B ³Π_g state. The rate coefficients for this process vary between 1E−11 cm³sec⁻¹ and 1E‐10 cm³sec⁻¹, with no measureable contribution by vibrational relaxation. The results suggest that production rates of the B ³Π_g state in the Lewis–Rayleigh (L–R) afterglow are much more uniformly distributed over the vibrational levels than has been previously assumed. We also suggest it is unlikely that significant amounts of energy pass through the ⁵Σ⁺_g state in the L–R afterglow. About 25% of the energy of atomic nitrogen recombination enters the B ³Π_g state in the L–R afterglow, according to the present results. The factors controlling the A ³Σ⁺_u v=0,1 population in the L–R afterglow appear to be much less well defined than has been suggested in previous literature.