Adsorption of NH2
Figure 6c and 6h shows NH2 adsorbed at its preferential
site – bridge. Supplementary Data Figure S4 shows the average spin
density before and after adsorption of NH2 to the
surface. On the (111) surface, the adsorption takes place on Ir atoms 5
and 6 as evidenced by the drop in spin density on those atoms. On the
(100) surface, bonding takes place on atoms 1 and 5 (B3LYP and B97-D3),
and 5 and 8 (B3LYP-D3). Again, the spin distribution per atom for each
method looks nearly identical after bonding.
Bond lengths in Table 5a are similar between methods, varying by at most
0.04 Å. EB3LYP > EB3LYP-D3> EB97-D3 for both surfaces.
Table 5b lists the vibrational modes of gas-phase and adsorbed
NH2.44,46,47 B3LYP and its
dispersion-corrected form match experiment for the symmetric mode
slightly better than B97-D3, while B97-D3 matches the asymmetric mode
best. On both the (111) and (100) surface, the scissoring mode is IR
active, while the symmetric stretch is strong and the antisymmetric
stretch is weak in Raman activity. The stretching mode between N and the
catalyst surface itself is very weak on both surfaces.