Fuel cell vehicles have been identified as the personal transportation technology of the future because of their high efficiency and very low emissions. To achieve the goal of road-ready fuel cell vehicles, great strides must be made in the development of fuel cells, hydrogen production and hydrogen storage technologies, that includes metal-H interaction studies and safety considerations. The interaction between two-hydrogen atoms and a gamma-Fe structure containing a vacancy has been studied using a cluster model and a theoretical method. For the study of the sequential absorption, the hydrogen atoms were positioned in their energy minima configurations, near the vacancy. The interactions mainly involve Fe 4s-H 1s atomic orbitals. The contribution of Fe 4p and Fe 3d orbitals is much less important. The Fe-Fe bond is weakened as new Fe-H-H and H-H pairs were formed. The effect of H atoms is limited to its first Fe neighbors. The Fe-Fe bond strength decreases with the introduction of the H atoms. Fe-H bonding is achieved at expense of weakening the metal-metal nearest bonds. There is not a real bond between the H atoms but some H-H interaction is observed. The detrimental effect of H atoms on the Fe-Fe bonds can be related to one of the aspect of embrittlement in gamma-Fe. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.