Time-resolved optical absorption measurements of excited-atom concentrations in the argon afterglow

Abstract

Diffusion coefficients, de-excitation cross sections and three-body collision coefficients for argon atoms in the 3p54s configuration have been obtained from optical absorption measurements of the relative decay rates of excited atoms following a pulsed discharge. The diffusion coefficients for the 1s5 and 1s3 metastable levels are D3 = 18 × 1018 cm-1 s-1, D5 = 17 × 1018 cm-1 s-1. Two-body de-exciting collisions involving an excited atom and a ground-state atom have cross sections of 10 × 10-19 cm2 for the 1s3 state and 18 × 10-20 cm2 for the 1s5 state. Three-body collisions involving the excited atom and two ground-state atoms have rate coefficients of 114 × 10-32 cm6 s-1, and 170 × 10-32 cm6 s-1 for the 1s3 and 1s5 levels respectively. The lifetime of the 1s4 state is greatly enhanced by resonance-radiation trapping and the early decay of this level has been measured and analysed using Holstein's theory to give a natural lifetime of 95 × 10-9 s.