Detailed measurements of fragment kinetic energy spectra coming from the interaction between intense 10.6 µm laser pulses and hydrogen and deuterium molecules have been made. Both the proton and the deuteron spectra exhibit a broad continuum distribution with a finer peak structure superimposed. These fragments are associated with the dissociation stage of the interaction. The broad continuum is understood using a simple two-step model in which the first stage involves the barrier-suppression dissociation of the molecular ion followed by a second step involving the interaction between the dissociated, charged fragment and the electric field. This model is analogous to the 'Simpleman theory' (van Linden van den Heuvell and Muller 1988 Multiphoton Processes, Cambridge Studies in Modern Optics vol 8 ed S J Smith and P L Knight (New York: Camridge University Press)) which has been used in the interpretation of long-wavelength above-threshold ionization results (