THERMAL-DECOMPOSITION OF COCL2

The thermal decomposition of COCl2 has been studied in incident shock waves at three different loading pressures and varying [COCl2]0. The k inetics experiments were performed at temperatures between 1400 and 20 00 K by monitoring the product Cl atoms using the atomic resonance abs orption spectrometric (ARAS) technique. Two decomposition pathways for COCl2 are possible: (1) COCl2 (+M) --> COCl + Cl (+M) and (2) COCl2 ( +M) --> CO + Cl2 (+M). The branching ratios were observed to be 90.5% and 9.5%, respectively. Second-order analysis for the sum of (1) and ( 2) gave the rate expression k(d)/[Kr] = (8.0 +/- 3.8) X 10(-8) exp(-30 549 +/- 766 K/T) cm3 molecule-1 s-1, with an error of +/- 35% at the o ne standard deviation level. This expression compares favorably to res ults from the decompositions of CH3Cl, CH2Cl2, and CC14 and provides e vidence to suggest that the DELTAH-degrees10 is in the range 70-80 kca l mol-1. Theoretical analysis has also been applied to reaction 1 usin g Troe's semiempirical methods. The best overall fit is obtained with DELTAH-degrees10 = 74.5 +/- 1.0 kcal mol-I and DELTAE(down) = 1714 cm- 1. This DELTAH-degrees10 implies DELTA(f)H-degrees (0 K) - -6.3 +/- 1. 0 kcal mol-1 for COCl. Similar theoretical analysis for reaction 2 sug gests a barrier height of 81.35 kcal mol-1.