EXCITATION OF 2P LEVELS 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 2p(1) to 2p(9 ), by measuring intensities of light originating from 2p levels and de caying to 2s levels. The excitation coefficients were obtained from th e optical signal at the anode of Townsend Ar discharges, after correct ion for the detector quantum efficiency. Measurements were done for wi der ranges of E/N from 50 Td to 9 kTd, than previously reported. Compa risons of our data with other experiments and calculations show differ ent effects of collisional energy transfer for different 2p levels at low E/N (pressure above 5 Torr). A comparison of the measured total ex citation coefficient for 2p levels with the Boltzmann calculations of electron excitation of 2p levels from the ground state and via cascadi ng shows the influence of collisional quenching to Is levels at the lo wer end of the E/N range and strong cascading from higher levels at hi gh E/N.