A technique for the first atomic resonance detection of ground state F 2p⁵²P_J atoms in a flow system is described. Collimated hole structures were used in place of windows to separate the lamp, flow tube and spectrometer. Resonance absorption measurements of the 3s–2p⁵ multiplet transition of F, between 95 and 98 nm, were used to obtain the first values for the oscillator strengths f_ik of the 97.39 nm ⁴P–²P and the 97.77 nm ⁴P–²P_½ lines of these multiplets. The values, which have an estimated standard error of ±30 %, are : f_ik(97.39)= 4 × 10^–5; f_ik(97.77)= 1 × 10^–5.

Fluorine atom resonance fluorescence in the 3s²P_J–2p⁵²P_J multiplet, and in one line of the 3s⁴P_J–2p⁵²P_J multiplet, was observed for the first time; it was used to measure concentrations of [F ²P_J] atoms down to 1 × 10¹¹ cm^–3. Measurement of absolute [F²P_J] was by means of the rapid reactions (1) and (2), F + Br₂ [graphic omitted] BrF + Br (1), F + Cl₂→ ClF + Cl. (2), Attenuation of F atom resonance fluorescence was used to measure the rate constant k₁ at 300 K. Combining this value with another (mass spectrometric) determination of k₁, the mean value k₁=(2.2 ± 1.1)× 10^–10 cm³ molecule^–1 s^–1 from 298 to 300 K was obtained.