  We investigate and discuss how hydrogen behaves at the edges of a graphite
sheet, in particular the armchair edge. Our density functional theory-based
calculations results show that, in contrast to the zigzag edge [cf., e-J. Surf.
Sci. Nanotech. 2 (2004) 77], regardless of orientation, there is an activation
barrier hindering H_2 dissociation at the armchair edges. And once they do get
dissociatively adsorbed at the armchair edges, we find that it would be
extremely hard to desorb the H from their adsorption sites at the armchair
edges. Furthermore, we also found that, consistent with our earlier conclusions
[cf., J. Phys. Soc. Jpn. 72 (2003) 1867], it is unlikely that we would find a
whole H_2 in between plain graphite sheets.
