Tunneling dynamics and spatial correlations of long chain growth in solid-state photochlorination of ethylene at low temperatures

A novel method is described for preparing reactive mixed crystals by vapor deposition in argon and subsequent evaporation of the argon. The kinetics of photochlorination chain reactions of ethylene-chlorine mixtures prepared by this method have been studied by dynamic UV and IR spectroscopy. Activationless chain growth occurs with mean length 260±70 in the temperature range 17–45 K. Chain lengths greater than 100 are observed up to 60–70% conversion to products. Comparison of the experimental data with computer simulations shows that the tunneling reaction is due to formation of a close-packed reaction complex with high amplitude zero-point vibrations which lower the vibrationally adiabatic barrier to reaction. The commensurability of reactant and product crystal lattices results in linear propagation of long chains without accumulation of deformation strain. Spatial correlations caused by nonlinear propagation are considered.