Atomic Electron Correlation in theMCapture ofAr37

The first experimental evidence for electron correlation in nuclear electron-capture ratios is reported. The measured $\frac{M}{L}$ capture ratio of ${}_{}{}^{37}{}_{}{}^{}\mathrm{Ar}$, 0.073±0.007, is inconsistent with Hartree-Fock calculations, but can be explained by final-state correlation, if the disputed $3s3p^6$ assignment in Cl i is adopted. The discrepancy in the experimental $\frac{K\beta }{K\alpha }$ x-ray intensity ratio of Cl is removed, and the designation of $L_{23}$ x-ray and $3s$ photoemission satellites in Cl is revised.