Electric quadrupole and magnetic dipole transition probabilities within the ground configuration of F⁺

The radiative lifetime of the 2s²2p^{4 1}S₀ level in F⁺ has been measured by time-resolved observations of both strong (though electric-dipole forbidden) decay branches: the electric quadrupole (E2) transition (≈80% branch) to the 2s²2p^{4 1}D₂ level and the magnetic dipole (M1) transition (≈20% branch) to the 2s²2p^{4 3}P₁ level. We observed the fluorescence associated with both transitions from a population of F⁺ ions circulating in a heavy-ion storage ring. Our result for the F⁺ 2s²2p^{4 1}S₀ level lifetime of 420±12 ms provides a benchmark for theory. Moreover, although the calculated lifetimes vary by more than 20%, the calculated branching fractions vary by less than 4% and 7% for the ¹S₀⃗¹D₂ E2 and ¹S₀⃗³P₁ M1 transitions, respectively. Using our measured lifetime and the calculated branching fractions, we report semiempirical transition probabilities for the ¹S₀⃗¹D₂ E2 and ¹S₀⃗³P₁ M1 transitions of 1.90 s^-1±7% and 0.50 s^-1±9%, respectively.