On the production and the decay of delayed molecular ultraviolet radiation in rare gas Townsend discharges

Abstract

We have studied the radiation produced in pre-breakdown discharges in Ar, Kr, and Xe, in a coaxial geometry, in the pressure range 50-600 torr. In these discharges, consisting of a single Townsend avalanche, radiation continues to be emitted for an appreciable time (up to some tens of microseconds) after the end of the current pulse. The intensity of the uv component of the radiation pulse is well expressed by a formula of the type I(t)similar, equals exp (−λ1t) −exp (−λ2t), where λ1 and λ2 are specific decay times. λ1 is a function of the pressure; λ2 is almost pressure independent.The results are discussed on the assumption that excited dimers are formed in the avalanche by three-body conversion of metastable atoms. The three-body conversion frequency for the dimer formation is 6·6×10−33 cm6s−1 for Arm, 44×10−33 cm6s−1 for Krm and 25×10−33 cm6s−1 for Xem. The mean lifetime for the excited dimers is 3·7 μs for Ar2*, 1·7 μs for Kr2* and 0·5 μs for Xe2*. At the lower pressures, two-body collisions become a relatively important destruction mechanism for the metastable Xe levels.