Rate coefficients for the dissociation of Kr-2(+), N2Ar+, (CO)(2)(+), CH5+, and C2H5+ ions in collisions with He have been obtained in a drift tube experiment as dependent on the mean relative kinetic energy in the center-of-mass frame E(c) in the range from 0.1 to 0.5 eV. The Arrhenius activation energies obtained for dissociation ar 1.15, 0.91, 1.1-1.3, 1.1-1.4, and 1.3-1.7 eV for Kr-2(+), N2Ar+, (CO)(2)(+), CH5+, and C2H5+ ions, respectively. For the thermal energy region, the rate coefficients for the same processes have been calculated from three-body association rate coefficients reported in the literature, equilibrium constants, and known thermodynamic quantities. The values of the dissociation rate coefficients obtained cover a range of 15 to 50 orders of magnitude. The present data indicate that the internal temperature T-i of the drifting ions is in close equilibrium with E(c), i.e., E(c)=3/2.k(B)T(i).