Non-reversed source of Br atom resonance radiation and its application to the measurement of Br atom concentrations

Abstract

Bromine atom resonance radiation, emitted following collisions of Br₂ with Ar*³P_2,0 metastable atoms, has been investigated. Depending on whether the excited Br atom emitters produced have been thermalised to room temperature, or are still translationally hot, Doppler and Biondi models for the Boltzmann or non-thermalised Br atom emitters can be used to interpret measurements of integrated absorption intensity as a function of Br 4p⁵²P ground state atom concentration. Nuclear hyperfine splitting of the resonance transitions, which contributes to line broadening, was included in the models. The results show that, for the non-reversed Ar*+ Br₂ resonance lamp, absorption intensity may be used to determine absolute Br atom concentrations with the use of the appropriate oscillator strength. Some new oscillator strength data for Br are reported. The measured Br atom resonance line oscillator strengths are shown to be insensitive to the translational kinetic energy of the Br emitter, because nuclear hyperfine splitting is the dominant line broadening mechanism at energies < 1 or 2 eV. The 157.7 and 131.7 nm resonance lines of Br are the most suitable for measurements of high (> 2 × 10¹³ cm^–3) and low (< 3 × 10¹² cm^–3) concentrations of Br using the Ar*+ Br₂ lamp.

Chlorine atom concentrations may be measured using resonance absorption with the similar Ar*+ Cl₂ chlorine atom resonance lamp; the 139.0 nm line is found suitable for [Cl] extending above 10¹⁴ cm^–3. Resonance absorption or fluorescence using the 139.0 nm line is also suitable for the determination of [Cl] using a microwave-excited chlorine resonance lamp.

These methods of determining Cl and Br atom concentrations are applicable to mixtures of atoms, produced for example by the rapid reaction of Br₂ with an excess of Cl atoms formed by microwave dissociation Cl₂: Cl + Br₂→ BrCl + Br, followed by Cl + BrCl → Cl₂+ Br; overall 2Cl + Br₂→ 2Br + Cl₂.