E1- M1 Damping Interference in the Electric Field Quenching of Metastable Ar¹⁷⁺ Ions

We have confirmed the prediction of a pseudo-time-reversal-odd anisotropy proportional to E⃗̇k̂ in the decay of metastable (2s_1/2) Ar¹⁷⁺ ions in an electric field E⃗, where k̂ is the direction of observation. The anisotropy arises from interference between the M1 and induced E1 amplitudes for the decay. Theory predicts that the pseudo-T-odd invariant should contribute to the angular distribution through a term associated with the damping (finite lifetime) of the 2p levels. The decay rate for the interference term is found to be -1.64(0.12) s^-1sr^-1(V/cm)^-1. This corresponds to a 2s Lamb shift for Ar¹⁷⁺ of 38.6(1.4) THz.