Trapping of Non-Resonance Radiation in Atoms and its Influence on Measured Lifetimes of the 4p and 5p Levels in Ar I

Lifetimes of 17 levels of the 3 p 5 4 p and 3 p 5 5 p 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 4 p , 5 p → 4 s (non-resonance) transitions are subjected to trapping effects which occur because of exceptionally long lifetimes of the 4 s levels due to either 4 s → 3 p resonance trapping (4 s, J = 1) or metastability (4 s, 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.