Yeah, bond energy itself is going to be the same regardless of isotope (or at least a negligibly small difference), so my guess is whatever mechanism that is ki

Yeah, bond energy itself is going to be the same regardless of isotope (or at least a negligibly small difference), so my guess is whatever mechanism that is kicking the hydrogen free is relying something more like a kinetic recoil from the photon where the mass is far more relevant. Of course, without being able to take a proper look under the hood at how they're actually storing the hydrogen, this is all rank speculation.