Guided ion beam kinetic energy thresholds in the ion-molecule reactions MH2 yields MHH where M is a closed-shell atomic ion B, Al, or Ga, were found to exceed by 0.4 to c.a. 5 ev the thermodynamic energy requirements or the theoretically computed barrier heights for these reactions. In addition, the formation of MD occurs at a significantly lower threshold than MH when M reacts with HD. Moreover, the measured reaction cross-sections for the production of MH or MD product ions are very small 10exp -17 to 10 exp -20sq cm being largest for B and smallest for Ga . A previous paper from this group proposed that collisional-to-internal energy transfer is the rate-limiting step for this class of reactions. It also suggested, based on a dynamical resonance picture, that collisions occurring at or near C2v symmetry are more effective than other collisions even though C2v geometries provide no lower potential energy barriers than others.