Table 2. Results of DFT Calculations Performed for This Work: Harmonic Frequencies for NH3* at the Most Stable Binding Site (On-Top) and on the Transition State (TS) for Hopping (Bridge) Obtained from a 4 × 4 [ 2 × 2 ] Supercell Using the PBE Exchange-Correlation Functionala.
| mode |
calculated
harmonic frequencies/cm–1 |
||
|---|---|---|---|
| vi (vgas) | description | on-top | TS for hopping (bridge) |
| v1 (3a) | asym. stretch | 3483.1 [3484.4] | 3546.7 [3550.5] |
| v2 (3b) | asym. stretch | 3481.5 [3482.8] | 3540.1 [3545.6] |
| v3 (1) | sym. stretch | 3356.8 [3342.7] | 3400.6 [3397.4] |
| v4 (4a) | asym. bending | 1572.5 [1551.3] | 1583.3 [1586.8] |
| v5 (4b) | asym. bending | 1571.5 [1549.7] | 1581.3 [1577.9] |
| vumb (2) | umbrella mode | 1142.0 [1055.2] | 930.0 [856.2] |
| free C3-axis rotation | - [ - ] | - [ - ] | |
| Rx | frustrated rotation | 672.7 [636.3] | 325.8 [131.3] |
| Ry | frustrated rotation | 672.4 [636.3] | 269.9 [109.5] |
| Tz | hindered translation | 357.8 [338.3] | 127.5 [ 45.9 ] |
| Tx | hindered translation | 122.8 [109.5] | 190.9i [176.4i] |
| Ty | hindered translation | 119.9 [109.5] | 68.2 [-] |
a
The imaginary frequency in Tx at the TS emerges from the degeneracy with the hopping coordinate. In this work we numbered the internal modes of adsorbed NH3 from high to low frequency. The conventional nomenclature from gas-phase vibrational spectroscopy is provided in parentheses for convenience.