Time-resolved gas-phase kinetic study of the germylene addition reaction, GeH2 + C2D4, as a function of temperature and pressure: isotope effects and mechanistic complexities

Abstract

Time-resolved studies of germylene, GeH2, generated by laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reaction with C2D4. The reaction was studied in the gas phase, mainly at a total pressure of 10 Torr (in SF6 bath gas) at five temperatures in the range 295–554 K. The second-order rate constants gave the Arrhenius equation: log(k∞/cm3 molecule−1 s−1) = (−10.76 ± 0.06) + (5.79 ± 0.46 kJ mol−1)/RT ln10Pressure variation measurements over the range 1–100 Torr (SF6) at 295, 406 and 554 K showed the rate constants to be pressure independent within experimental error. Comparison with the reaction of GeH2 + C2H4 studied earlier, which was pressure dependent, gave large inverse isotope effects which increased with increasing temperature and decreasing pressure. The data supports a mechanism, involving the reversible isomerisation of initially formed germirane-d4 to ethylgermylene-d4 and is consistent with previously carried out thermochemical and ab initio calculations of the energy surface.