Measurement of ground state 2P bromine and chlorine atom concentrations in discharge-flow systems

Abstract

Methods for the measurement in discharge-flow systems at 300 K of concentrations of ground state ²P Cl and Br atoms were investigated. Reactant and product stoichiometries in the two sequences of rapid reactions (I) and (II) have been measured: (I) 2O + Br₂→ 2Br; + O₂(1), Br + ClNO → BrCl + NO (2), (II) 2O + OClO → Cl + 2O₂(3), Cl + ClNO → Cl₂+ NO (4), [O], [Cl] and [Br] were monitored with resonance line absorption. [NO] was measured by resonance absorption in the (1,0) band of the NO ε-system D²Σ⁺–X²Π. On-line mass spectrometry was used for the measurement of [NO], and [BrCl].

The observed stoichiometries were as follows, using the reactions (1) and (3) with excess [O] as sources of known [Br] and [Cl]. (i) In reaction (2), ([NO]produced)/([Br]reacted)=(1.06 ± 0.11); ([BrCl]produced)/([Br]reacted)=(0.94 ± 0.09). (ii) In reaction (4), ([NO]produced)/([Cl]reacted)=(1.04 ± 0.06). Measurements by resonance absorption of ([NO]produced) in reactions (2) and (4) with excess ClNO lead to concentrations of Cl and Br ²P atoms with a standard error of ±5 % in a wide concentration range. Mass-spectrometric detection of NO and BrCl in reactions (2) and (4) is considered slightly less accurate.