Time-resolved gas-phase kinetic study of the germyleneaddition reaction, GeH2 + C2D2

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 coefficients for its bimolecular reaction with C₂D₂. The reaction was studied in the gas phase, mainly at a total pressure of 1.3 kPa (in SF₆ bath gas) at five temperatures in the range 298–558 K. Pressure variation measurements over the range 0.13–13 kPa (SF₆) at 298, 397 and 558 K revealed a small pressure dependence but only at 558 K. After correction for this, the second-order rate coefficients gave the Arrhenius equation:log(k^∞/cm³ molecule⁻¹ s⁻¹) = (−10.96 ± 0.05) + (6.16 ± 0.37 kJ mol⁻¹)/RT ln 10Comparison with the reaction of GeH₂ + C₂H₂ (studied earlier) showed a similar behaviour with almost identical rate coefficients. The lack of a significant isotope effect is consistent with a rate-determining addition process and is explained by irreversible decomposition of the reaction intermediate to give Ge(³P) + C₂H₄. This result contrasts with that for GeH₂ + C₂H₄/C₂D₄ and those for the analogous silylene reactions. The underlying reasons for this are discussed.