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 cryocrystals by deposition of argondiluted reactant beams and subsequent crystallization during evaporation of the inert gas. Photochlorination of equimolecular ethylene—chlorine mixtures obtained by this method and studied by means of kinetic UV- and IR-spectroscopy reveals activationless chain growth with mean length 300 units in the temperature range 17–45 K. Mean chain lengths greater than 100 are observed up to the conversion degree of 0.6–0.7. Comparison of the experimental data with computer simulations shows that the tunneling reaction is due to the formation of a closely packed reaction complex with high amplitudes of zero-point vibrations which lower the reaction barrier. The commensurability of reactant and product crystal lattices results in linear propagation of chains without accumulation of deformation strain. The chain termination mechanism associated with the spatial correlations of chains is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 687–700, April, 1993.The authors are grateful to Academician V.I. Goldanskii, Dr. D.E.Makarov, and Prof. S. Sato for useful discussion and to A.U.Goldschleger for assistance with the experiments.