Reaction kinetic studies of CCl2 (X̃(0,0,0)) with C2H2 and H2O molecules

Abstract

Abstract Absolute reaction rate constants for the ground state dichlorocarbene CCl2 with C2H2 and H2O have been measured (T=293 K). The CCl2 radicals were produced by laser photolysis of CCl4 molecules at 213 nm and then electronically excited to the CCl2 ( A ) state at 541.0 nm with Nd:YAG laser pumped dye laser. The technique of laser-induced fluorescence was employed to measure the relative concentrations at different reaction time and, then, obtain their rate constants. They are (3.3 ± 0.5) × 10−13 cm3 molecule−1 s−1 for the reaction of CCl2 + C2H2 and (4.8 ± 2.0) × 10−14 cm3 molecule−1 s−1 for the reaction of CCl2 + H2O (total pressure=12 Torr, T=293 K), respectively. It is found that the rate constant for reaction CCl2 + C2H2 slightly increases with the total pressure (P=10–50 Torr). But for the reaction CCl2 + H2O, it is independent on the total pressure. The mechanisms for these two reactions have been theoretically studied using a high-level ab initio calculation. For the reaction of CCl2 + H2O, it is found that there are two reaction mechanisms: insertion and addition-elimination. Three primary product channels, HCl + HClCO, HCl + trans-ClCOH and HCl + cis-ClCOH, are studied in detail. For the reaction of CCl2 + C2H2, there are also two reaction mechanisms: insertion and three-cyclo-addition. The addition of C atom in CCl2 radical to C–C triple bond in C2H2 molecule may be the dominant reaction channel giving a three-member-ring structure, CCl2 CHCH radical, as the primary intermediate.