Chemiluminescent titration of F(g) with Cl2(g) and microwave production of atomic fluorine

Abstract

Chemiluminescent titration of atomic fluorine with Cl₂ in a low pressure (133 Pa) flow apparatus has been investigated to establish the accuracy of this titration method and the efficiency of F atom production in a microwave discharge. Up to 90 % dissociation of F₂(0.5–10 % in Ar) is achieved by a 100 W Evenson-type cavity 2450 MHz discharge when the microwave power exceeds 2500 kJ mol^–1 F and discharge residence time exceeds 0.7 ms. Heterogeneous F atom loss on the fluorine-passivated Al₂O₃ discharge tube walls occurs with a recombination probability, γ_F≈ 2 × 10^–4. Heterogeneous Cl atom recombination does not interfere with the chemiluminescent F/Cl₂ titration in glass apparatus since, in the presence of fluorine, γ_Cl(pyrex) < 8 × 10^–5. However, homogeneous three-body recombination to form ClF and/or Cl₂ produces errors in the titration endpoint which exceed 10 % if the product of F atom partial pressure, total pressure and the mean residence time between titrant addition and chemiluminescent intensity measurement exceeds 160 Pa² s at 300 K.