EXPERIMENTAL AND TRANSITION-STATE THEORY STUDIES OF THE GAS-PHASE REACTIONS OF ALCL WITH N2O, CO2, AND SO2

The high-temperature fast-flow reactor technique has been used to make kinetic measurements. A weighted fit to the AlCl + N2O data gives k(700-990 K) = 5.6 x 10(-11) exp(-7380 K/T) cm3 molecule-1 s-1. A weighted fit to the AlCl + CO2 Measurements leads to the expression k(900-1790 K) - 4.4 x 10(-23) (T/K)3.0 exp(-3900 K/T) CM3 molecule-1 s-1. 2sigma accuracy limits are about +/- 25%. An upper limit k(800-1100 K) < 5 X 10(-14) CM3 molecule-1 s-1 has been determined for the AlCl + SO2 reaction. An alternate form of classical transition-state theory is developed to allow predictions on the preexponential part of mte coefficient expressions for metallic species. This model-based transition-state-theory (MTST) method uses a valence-force molecular model to estimate rotational constants and vibrational frequencies of the transition state and is applicable to reactions with early barriers, typical of many exothermic charge-transfer reactions. The geometrical parameters and force constants that describe the molecular model are derived from properties of the reactants. For the N2O reaction good agreement between MTST and experiment is obtained, based on the assumption of an 0 atom abstraction reaction leading to OAlCl. No such agreement is found for the CO2 reaction, which indicates adduct formation as the main AlCl consumption channel. For the previously measured AlCl + O2 reaction MTST calculations suggest that abstraction can be of some significance above about 1500 K; however, adduct formation appears to dominate over most of the 490-1750 K range.