The kinetics of the title reaction have been investigated at 296 K (3-400 Torr in Ar and 3-50 Torr in SF6), and between 298 and 434 K (5 Torr in Ar). The second-order rate constants increase by ca. x 20 between 3 and 400 Torr (Ar) and ca. x 6 between 3 and 50 Torr (SF6). At 5 Torr Ar, an Arrhenius plot gives log(A/cm(3) molecule(-1) s(-1)) = -13.71 +/- 0.13 and E-a -15.3 +/- 0.9 kJ mol(-1). The data are consistent with the formation of an H2Si . . . OMe2 donor-acceptor adduct. RRKM/master equation modelling of the rate constants at 296 K gives a high pressure limiting value (k(proportional to)) of 6.6 x 10(-10) cm(3) molecule(-1) s(-1) and a binding energy of 96 kJ mol(-1) for the adduct.