Measurement of the lifetime of the3 P 2 and4 P 5/2 states in Ar16+ and Ar15+

Promptly decaying levels in Li- and Be-like Ar could be identified in the delayed x-ray and electron spectrum in addition to the four known metastable (1s2s)¹ S ₀, (1s2s)³ S ₁, (1s2p)³ P ₂, and (1s2s2p)⁴ P _5/2 states in He- and Li-like systems. The states having lifetimes of about 10^?14s still contribute to the spectrum observed 10^?9s after the ions have passed a foil. This observation is explained by cascading processes from states of high principal quantum numbern≧14. The measured lifetime of the⁴ P _5/2 state subtracting the contribution of cascades is (0.594±0.016) ns and slightly larger than the theoretically predicted value of 0.563 ns. The³ P ₂ state is depopulated at short distances behind the foil by cascading processes. Its measured lifetime of (1.44±0.08) ns compares to a theoretical value of 1.48 ns.