Absolute Electron Collision Cross Sections for Two Forbidden Transitions in Nitrogen at Kinetic Energies of 300–500 eV

Absolute differential electron collision cross sections and generalized oscillator strengths have been measured for two forbidden transitions, $a^1{\Pi }_g{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}X}}^1{\Sigma }_g^{+}$ and ${\mathrm{a″}}^1{\Sigma }_g^{+}{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}X}}^1{\Sigma }_g^{+}$ , in N₂. These measurements were carried out at electron kinetic energies of 300, 400, and 500 eV and at small scattering angles $\text{(θ\hspace{0.17em}=\hspace{0.17em}2°–6°)}$ to facilitate extrapolation to zero momentum change. The Born approximation apparently holds for the excitation of the first transition but not for the second. Generalized oscillator strengths, however, extrapolate to the optical oscillator strength (zero) in both cases in accord with the limit theorem previously demonstrated.