Excitation of several important metastable states of N2 by electron impact

Absolute cross sections for excitation of the A³Σᵤ⁺, $a^1{\Pi }_q$, and $E^3{\Sigma }_g^{+}$ metastable states of N₂ were deduced from previous time-of-flight studies of metastable nitrogen molecules. The cross section for direct excitation of the A³Σᵤ⁺ state was determined from threshold to 40 eV and was found to have a peak value of (${5.3}_{-3.0}^{+4.0}$) × 10⁻¹⁷ cm² near 11 eV. The total apparent cross section of the A³Σᵤ⁺ state was obtained by adding cascade contributions from the $B^3{\Pi }_g$ and $C^3{\Pi }_u$ states and was found to have a value of about 1.2 × 10⁻¹⁶ cm² at the two peaks near 11.0 and 14.5 eV. The $E^3{\Sigma }_g^{+}$ state was efficiently excited near threshold and exhibited a resonancelike excitation function with a half-width (full width of half-maximum) at about 0.4 eV and a peak cross section of (7.0 ± 4.0) × 10⁻¹⁸ cm² at 12.2 eV. The excitation function for the $a^1{\Pi }_g$ state was obtained from threshold to about 40 eV and was found to differ markedly from two other measurements. Using the present results, a sample vibrational distribution for noninteracting molecules in the A³Σᵤ⁺ state was calculated at selected electron energies near threshold. For most energies, the lowest vibrational levels are most strongly populated in qualitative agreement with atmospheric observations.