1. 4.26 eV
2.94 eV 1 2 3 4 5 6 7
Potential energy surface illustrating an H-atom attachment to a sp2 C with two C and one H neighbors. The light blue spheres indicate sp3-hybridized C atoms, the dark red spheres indicate sp2-hybridized C atoms, and the relatively small cyan spheres indicate H atoms. The C atom to which the incoming H atom gets attached and its first and second neighbors are labeled numerically. The exothermic energy of each reaction event is also indicated. In the first step H atom attaches to a sp2 C atom and a dangling bond is created on its first neighboring sp2 C atom and both C atoms are converted to sp3 C atoms. In the second step a neighboring C-C bond between the C atom to which H atom gets attached and its first neighbor is broken and both C atoms get converted back to sp2 C atoms.