The transition probability of the magnetic dipole $\mathrm{}\left(M1\mathrm{}\right)\mathrm{}$ transition ${2s}^{2}2p$ ${}^2{P}^o$ $J=1/2\mathrm{}$ to $J^{\prime }=3/2\mathrm{}$ $(\lambda =574.19\mathrm{}\mathrm{nm})$ in the B-like ion ${\mathrm{Cl}}^{12+}$ has been measured using two different light sources, the Heidelberg heavy-ion storage ring TSR and the Livermore electron-beam ion trap EBIT-I. Our results for the atomic level lifetime are $21.2\pm 0.6\mathrm{ms}$ from the heavy-ion storage ring and $21.0\pm 0.5\mathrm{ms}$ from the Livermore electron-beam ion trap. Particular attention has been paid to systematic errors, making this experiment a common reference for atomic level lifetime measurements in the visible spectrum.

• Received 25 June 2002

DOI:https://doi.org/10.1103/PhysRevA.66.052507