A Bendix time of flight mass spectrometer has been modified to enable the determination of some ion-molecule reaction cross sections in the energy range 1 — 100 eV. In the reactions studied X+ + D2 → XD++D where X may be Ar, N2 or CO, the results obtained agree with the predictions of the polarization theory in the range below 10 eV despite the fact that no intermediate complex is formed at these energies. Between about 10—50 eV where spectator stripping occurs the cross section follows an approximate E-l dependence. Above these energies the results are consistent with a transition to a region in which knock-on processes predominate and where an impulse approximation treatment would be valid.