THERMAL-DECOMPOSITION OF CF3BR USING BR-ATOM ABSORPTION

Br-atom atomic resonance absorption spectrometry (ARAS) has been devel oped and applied to measure thermal decomposition rate constants for C F3Br (+ Kr) --> CF3 + Br (+ Kr) over the temperature range, 1222-1624 K. The Br-atom curve-of-growth (145 < lambda < 163 nm) was determined using this reaction. For [Br] less than or equal to 1 x 10(12) molecul es cm(-3), absorbance, (ABS) = 1.410 x 10(-13) [Br], yielding sigma = 1.419 x 10(-14) cm(2). The curve-of-growth was then used to convert (A BS) to Br-atom profiles which were then analyzed to give measured rate constants. These can be expressed in second-order by k(1) = 8.147 x 1 0(-9) exp(- 24488 K/T) cm(3) molecule(-1) s(-1) (+/-33%, 1222 less tha n or equal to T less than or equal to 1624 K). A unimolecular theoreti cal approach was used to rationalize the data. Theory indicates that t he dissociation rates are closer to second- than to first-order, i.e., the magnitudes are 30-53% of the low-pressure-limit rate constants ov er 1222-1624 K and 123-757 torr. With the known, E-0 = Delta H-0(0) = 70.1 kcal mole(-1), the optimized theoretical fit to the ARAS data req uires [Delta E](down) = 550 cm(-1). These conclusions are consistent w ith recently published data and theory from Kiefer and Sathyanarayana. (C) 1998 John Wiley & Sons, Inc.