The role of nonequilibrium effects on negative Arrhenius activation energyin a Lorentz gas

The perturbation method is used for solving the Boltzmann equation for a re active Lorentz gas for the chemical reaction A+B --> products. Analytical e quations for the Arrhenius activation energy E-A are derived for the revers ed Prigogine-Xhrouet and reversed line-of-centers models. The results are c ompared with numerical results obtained by Stiller et al. from the Lorentz- Fokker-PIanck equation. It is confirmed that the nonequilibrium effects can enlarge small negative values of E-A for reactions in which only the molec ules colliding with small relative velocities can react. If E-A = 0 in the nonequilibrium description the temperature of the system equals the Shizgal -Karplus temperature. (C) 1998 Elsevier Science B.V. All rights reserved.