Table & Figure Captions
Table 1. Cohesive energy of iridium clusters with n atoms, where n=10, 15, 20, 25, and 30. The ground state spin multiplicity was predicted using the Interstitial Electron model and verified by testing two multiplicities above and below the ground state. The lowest energy state is presented here for each cluster size.
Table 2a. Bond energies and bond lengths are given for the most favorable orientation of N2 on the (111) and (100) surfaces.
Table 2b. Vibrational modes and their corresponding frequencies (in cm-1) for free and adsorbed N2 on both the (111) and (100) surface. Values are compared to existing experimental and theoretical observation.aexperimental; btheoretical;cIR; dEELS; *index plane not specified
Table 3a. Bond energies and bond lengths are given for N at its lowest energy position – HCP for the (111) surface and bridge for the (100) surface.
Table 3b. Vibrational modes and their corresponding frequencies (in cm-1) for adsorbed N at its lowest energy position – HCP for the (111) surface and bridge for the (100) surface. The displacement of N for each stretching mode is labeled as either perpendicular or parallel to the cluster surface. Values are compared to existing experimental and theoretical observation.
atheoretical – RPBE
Table 4a. Bond energies and bond lengths are given for NH at its lowest energy position – HCP for the (111) surface and bridge for the (100) surface.
Table 4b. Vibrational modes and their corresponding frequencies (in cm-1) for free and adsorbed NH at its lowest energy position – HCP for the (111) surface and bridge for the (100) surface. The displacement of N in Ir-N the stretches is labeled as either perpendicular or parallel to the cluster surface. Values are compared to existing experimental and theoretical observation.
aexperimental;bIR; F-failed to converge
Table 5a. Bond energies and bond lengths are given for NH2 at its lowest energy position – bridge for both the (111) surface and (100) surface.
Table 5b. Vibrational modes and their corresponding frequencies (in cm-1) for free and adsorbed NH2 at its lowest energy position – bridge for the (111) and (100) surface. Values are compared to existing experimental and theoretical observation. Asymmetric and symmetric stretches are abbreviated as a. stretch and s. stretch.
aexperimental; bIR;cDifference Frequency Laser Spectroscopy
Table 6a. Bond energies and bond lengths are given for NH3 at its lowest energy position – top for both the (111) and (100) surface.
Table 6b. Vibrational modes and their corresponding frequencies (in cm-1) for free and adsorbed NH3 at its lowest energy position – top for the (111) and (100) surface. Values are compared to existing experimental and theoretical observation. Asymmetric and symmetric stretches are abbreviated as a. stretch and s. stretch.
aexperimental; btheoretical;cIR; *index plane not specified
Figure 1. Irn clusters modelled, where n=10,15, 20, 25, and 30. The left column depicts the (111) surfaces and the right column depicts the (100) surfaces. Atoms are numbered so they can be matched with their respective spin densities in Figure 2.
Figure 2. Spin density of Irn clusters (n=10, 15, 20, 25). Columns 1, 2, and 3 show the cluster spin densities using B3LYP, B3LYP-D3, and B97-D3 respectively. The 30-atom cluster only converged for the (100) surface at the B97-D3 level of theory, so it was not included in this comparison.
Figure 3. Preferential sites for adsorption on the (111) (above) and (100) (below) Ir15 surfaces. B=Bridge, T=Top, HCP=Hexagonal Close-Packed, FCC=Face-Centered Cubic, and H=Hollow.
Figure 4. Binding energy (based on electronic energies) of molecules adsorbed on the (111)[a-d] and (100)[e-h] surfaces using the three different functionals. B=Bridge, T=Top, HCP=Hexagonal Close-Packed, FCC=Face-Centered Cubic, and H=Hollow.
Figure 5. Binding energy (based on electronic energies) of N2 adsorbed on the (111) and (100) surfaces at various angles. Θ is the angle the N-N bond makes with the catalyst surface.
Figure 6. Top view of preferred adsorption sites for adsorbed N, NH, NH2, and NH3 on the (111)[a-d] and (100)[f-i] surface. A side view is given for N2 [e and j]. Images shown are from the B97-D3 optimizations, but site preferences are consistent across all methods. However, the orientation of N2 is different using B3LYP-D3.