Effect of cascade through circular Rydberg states and surface wakefield on the decay of n=2→n=1 transition of H-like V in beam–foil excitation

Abstract

Beam–foil spectroscopy is used to study the unresolved decay of short-lived 2p (τ2p≈5.3fs) and long-lived 2s (τ2s≈756.7ps) states of H-like V for the time range 25–400ps. We have observed a hump-like structure, peaked at ~145ps, in the decay of the 2p state riding on the decay curve of the 2s state. This unusual behavior is similar to the one reported by us recently in H-like Fe (Mishra AP, et al. J Quant Spectrosc Radiat Transfer 2013;120:114–9) and occurs as a consequence of the sequential cascading down of circular Rydberg states to the 2p state. More importantly, it is inferred in this paper that Nandi and Mohanty (Nandi T, Mohanty BP. J Phys B: At Mol Opt Phys 2009;42:225402), who attributed the drastic reduction in the observed lifetime of the 2s state in beam-foil excitation to Stark mixing of the 2s2S1/2 and 2p2P1/20 states due to the wakefield at the exit surface of the foil, had overestimated the Stark mixing parameter and the strength of the wake electric field responsible for the mixing at least by a factor ~5.5.