Excitation ofN2in dc electrical discharges at very highE/n

Spatial distributions of light emission from electric discharges in ${\mathrm{N}}_2$ have been measured at very high electric-field–to–gas-density ratios E/n and low gas densities. The E/n range was from 270 Td to 107 kTd at gas densities from 1.3×${10}^{23}$ to 1.5×${10}^{21}$ ${\mathrm{m}}^{\mathrm{-}3}$ (1 Td≡${10}^{\mathrm{-}21}$ V ${\mathrm{m}}^2$). Planar electrodes and low discharge currents, less than 3×${10}^{\mathrm{-}4}$ A/${\mathrm{m}}^2$, insured that the electric field was spatially uniform. At the lower E/n and near the anode the intensities of first negative ${(1\mathrm{}}^{\mathrm{-}}$) and first ${(1\mathrm{}}^{+}$) and second ${(2\mathrm{}}^{+}$) positive bands of ${\mathrm{N}}_2$ increased exponentially with distance as expected from published measurements of the spatial growth of ionization. The first and second positive band intensities were placed on an absolute scale by normalization to previously measured or calculated excitation coefficients for E/n of 270 to 700 Td.