The authors present measurements of the intensity and polarisation of light emitted from two excited states of neutral helium, after break-up of the HeH+ molecule in thin foils. The authors vary the foil thickness to study their dependence on the internuclear separation of the He and proton at the final foil surface and postulate that the variations observed are sensitive to the molecular orbitals of the dissociating HeH+ molecule. These vicinage effects provide the distance scale of the final state interaction at the foil surface.