$\mathit{E}1$- $\mathit{M}1$ Damping Interference in the Electric Field Quenching of Metastable ${\mathrm{Ar}}^{17+}$ Ions

We have confirmed the prediction of a pseudo-time-reversal-odd anisotropy proportional to $\overrightarrow{E}̇\hat{k}$ in the decay of metastable $\left({2s}_{1/2}\right){\mathrm{Ar}}^{17+}$ ions in an electric field $\overrightarrow{E}$, where $\hat{k}$ 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 $-1.64\mathrm{}\left(0.12\right){\mathrm{s}}^{-1\mathrm{}}{\mathrm{sr}}^{-1\mathrm{}}(\mathrm{V}/\mathrm{cm}{)}^{-1\mathrm{}}$. This corresponds to a 2s Lamb shift for ${\mathrm{Ar}}^{17+}$ of 38.6(1.4) THz.