Fluorine mean-life measurements below 1000 Å using the beam–foil technique

Abstract

We have used the beam–foil technique to measure mean lives for 16 transitions in F I–F IV in the wavelength region 400 Å–1000 Å. Good agreement is found with the results of recent calculations, particularly those employing correlated wave functions. The f-value trends for 5 isoelectronic sequences are presented in detail (2p^{5 2}P⁰–2p⁴3s² D and 2p^{5 2}P⁰–2p⁴3s ²P in F I; 2p^{4 3}P–2p³3s ³D⁰ in F II; 2p^{3 2}D⁰–2s2p^{4 2}D and 2p^{3 4}S⁰–2s2p^{4 4}P in F III). Our f value for the 955 Å multiplet in F I is also used in conjunction with some new satellite data to show that the fluorine abundance is apparently depleted in interstellar clouds by a factor of at least 3 below its solar value.