Reaction of H atoms with CH 2Cl 2application to the inhibition of flames

Abstract

The reaction kinetics of atomic hydrogen with dichloromethane have been investigated in adischarge-flow system in the 298°–460°K temperature range, and at total pressures near 1 torr. A quadrupole mass spectrometer was adapted for the simultaneous determination of atomic hydrogen and stable species concentrations. For the H+CH 2 Cl 2 over-all reaction, the stoichiometry[H] 0 −[H]/([CH 2 Cl 2 ] 0 −[CH 2 Cl 2 ]) determined for various initial [H] 0 /[CH 2 Cl 2 ] 0 ratios always exceeds 4. The products have been identified as HCl, H 2 , CH 4 , C 2 H 2 , and C 2 H 4 . The rate constant of the initial step, H+CH 2 Cl 2 →HCl+CH 2 Cl, was found to be k 1 =1.8×10 −11 exp(−6100/ RT ) cm 3 molecule −1 s −1 from 298° to 460°K. Evidence was found for the occurrence of secondary reactions,H+HCl→Cl+H 2 , Cl+CH 2 Cl 2 →HCl+CHCl 2 . The use of D atoms instead of H atoms gives further information on the reaction mechanism, which is discussed. Reaction (1) may be the inhibiting step in the mechanism of flame inhibition by CH 2 Cl 2 .