Excitation of 2plevels of argon in Townsend discharges at a high ratio of electric field to gas density

We have made measurements of the absolute emission intensities, i.e., excitation coefficients of 2p levels of argon atom, from 2${\mathit{p}}_1$ to 2${\mathit{p}}_9$, by measuring intensities of light originating from 2p levels and decaying to 2s levels. The excitation coefficients were obtained from the optical signal at the anode of Townsend Ar discharges, after correction for the detector quantum efficiency. Measurements were done for wider ranges of E/N from 50 Td to 9 kTd, than previously reported. Comparisons of our data with other experiments and calculations show different effects of collisional energy transfer for different 2p levels at low E/N (pressure above 5 Torr). A comparison of the measured total excitation coefficient for 2p levels with the Boltzmann calculations of electron excitation of 2p levels from the ground state and via cascading shows the influence of collisional quenching to 1s levels at the lower end of the E/N range and strong cascading from higher levels at high E/N. © 1996 The American Physical Society.