Abstract
Lifetimes of 17 levels of the 3p 5 4p and 3p 5 5p configurations in Ar I have been measured using the High Frequency Deflection technique at target pressures in the range 0.04-10 mtorr. An anomalous pressure dependence is found which indicates that the studied 4p, 5p → 4s (non-resonance) transitions are subjected to trapping effects which occur because of exceptionally long lifetimes of the 4s levels due to either 4s → 3p resonance trapping (4s, J = 1) or metastability (4s, J = 0, 2). A theoretical fit to the observed pressure dependence based upon this process is given as well as corrected zero pressure lifetimes which in several cases are considerably shorter than earlier published values.