Mean Life of the Metastable2 P13State of the Two-Electron Fluorine Ion

By measuring the radiative decay in flight of a foil-excited heliumlike fluorine beam, we have determined the lifetime of the metastable $2 {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of the two-electron ion ${\mathrm{F}}^{7+}$. Our data yield the singlet-triplet intercombination transition probability $A(1\mathrm{} {}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-2 {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{})=(1.77\mathrm{}\pm 0.10)\times {10}^9$ ${\sec }^{-1\mathrm{}}$, which is in excellent agreement with theoretical calculations of a strongly $Z$-dependent spin-orbit-induced electric dipole decay, and extends our earlier measurements for ions in this isoelectronic sequence. Because this transition is observed in the solar spectrum for all abundant heliumlike ions from carbon to iron, we also discuss the relevance of this measurement to solar physics.