An effect of temperature on kinetics and mechanism of the reaction RX + e -> R-center dot + X- is studied using molecular dynamics simulations method for two molecules: t-BuCl and t-BuBr in two different solvent viscosities gamma(x) =2 ps(-1) and gamma(x) = 40 ps(-1). The potential surfaces used in the simulations are two-dimensional and depend on the solvent generalized coordinate x and the C-X bond elongationy, the latter part based on quantum calculations. For both systems the transfer coefficient a is found to decrease with temperature and this effect is stronger in the more viscous solvent. For gamma(x) = 40 ps(-1) the following a values are reported: at T = 278 K 0.234 (t-BuCl) and 0.264 (t-BuBr), while at T = 398 K 0.208 (t-BuCl) and 0.222 (t-BuBr). In identical conditions and for the same height of the energy barrier, alpha(t-BuCl) is always lower than alpha(t-BuBr). The results are interpreted as an effect of the saddle point avoidance phenomenon. (C) 2011 Elsevier Ltd. All rights reserved.