Thermal decomposition of CF3Br using Br-atom absorption

Br-atom atomic resonance absorption spectrometry (ARAS) has been developed and applied to measure thermal decomposition rate constants for CF3Br (+ Kr)→CF3+Br (+ Kr) over the temperature range, 1222–1624 K. The Br-atom curve-of-growth (145<λ<163 nm) was determined using this reaction. For [Br]≤1×1012 molecules cm−3, absorbance, (ABS)=1.410×10−13 [Br], yielding σ=1.419×10−14 cm2. The curve-of-growth was then used to convert (ABS) to Br-atom profiles which were then analyzed to give measured rate constants. These can be expressed in second-order by k1=8.147×10−9 exp(−24488 K/T) cm3 molecule−1 s−1 (±33%, 1222≤T≤1624 K). A unimolecular theoretical approach was used to rationalize the data. Theory indicates that the dissociation rates are closer to second- than to first-order, i.e., the magnitudes are 30–53% of the low-pressure-limit rate constants over 1222–1624 K and 123–757 torr. With the known, E0=ΔH00=70.1 kcal mole−1, the optimized theoretical fit to the ARAS data requires 〈ΔE〉down=550 cm−1. These conclusions are consistent with recently published data and theory from Kiefer and Sathyanarayana.