Continuous-wave CO2 laser-induced chain reaction of 1,2-dichloroethane

Abstract

The chain reaction of 1,2-dichloroethane induced by a CW CO₂ laser has been studied in the presence of SF₆ as a sensitizer. Vinyl chloride and hydrogen chloride are the main products. The photosensitized decomposition of 1,2-dichloroethane mainly depends on the irradiated laser frequency and is governed by the excitation of the vibrational mode and collisional energy transfer. Arrhenius plots show two distinct regimes, corresponding to the respective activation energies: 96.3 kJ mol^–1 for the low-temperature regime and 50.2 kJ mol^–1 for the high-temperature regime. The inhibiting and promoting effects of propene and chlorine, respectively, on the chain reaction are examined. The kinetics proposed for the chain reaction are in agreement with the observed data, and mechanisms for molecular excitation and intramolecular energy transfer have been discussed. By using an IR laser, active centres can be generated, and initiation and propagation of a chain reaction at lower temperatures than is possible thermally can be achieved. This may be a way to decrease the energy expenditure and reduce the number of by-products in the chain reaction.