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(7 00-990 K) = 5.6 x 10(-11) exp(-7380 K/T) cm3 molecule-1 s-1. A weighte d fit to the AlCl + CO2 Measurements leads to the expression k(900-179 0 K) - 4.4 x 10(-23) (T/K)3.0 exp(-3900 K/T) CM3 molecule-1 s-1. 2sigm a 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 re action. An alternate form of classical transition-state theory is deve loped to allow predictions on the preexponential part of mte coefficie nt 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 st ate and is applicable to reactions with early barriers, typical of man y exothermic charge-transfer reactions. The geometrical parameters and force constants that describe the molecular model are derived from pr operties 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 c onsumption channel. For the previously measured AlCl + O2 reaction MTS T calculations suggest that abstraction can be of some significance ab ove about 1500 K; however, adduct formation appears to dominate over m ost of the 490-1750 K range.