Gas-phase reaction rate constants for the reaction of silylene, SiH2, with
dimethyl ether, CH3OCH3 have been determined over the temperature range 294
-441 K and at total pressures of inert bath gas (Ar or SF6) over the range
30-850 Torr. The second-order rate constants are pressure dependent, even u
p to the maximum pressure investigated of 850 Torr, and the rate constants
decrease with increasing temperature, indicating that the reaction proceeds
via the formation of a complex. At the highest temperature studied (441 K)
, the experimental decay curves do not return to the baseline. This is attr
ibuted to the system reaching equilibrium, with SiH2 being produced by diss
ociation of the complex, and provides direct experimental evidence for the
formation of the complex. Analysis of the decay curves provided an experime
ntal determination of the equilibrium constant, K-eq, at 441 K. The high-pr
essure rate constants, obtained by extrapolation of the experimental data u
sing RRKM/master equation modelling, yield the Arrhenius parameters log (A/
cm(3) molecule(-1) s(-1))=-7.6 +/-0.4 and E-a=9.3 +/-2.8 kJ mol(-1). The RR
KM/master equation modelling gives a well depth for the SiH2-CH3OCH3 comple
x of 87 kJ mol(-1). This compares with a value of 88.4 +/-1.7 kJ mol(-1) de
termined from K-eq at 441 K. Ab initio calculations, performed at the MP2/6
-311+G** level of theory, give a well-depth for the complex of 82.9 kJ mol(
-1), in excellent agreement with this value.