Table 1. Calculated anharmonic (VPT2) band positions (in cm–1) of trans-formic acid alongside calculated diagonal (italics) and off-diagonal anharmonicity constants x2i, x3i, and x6i (in cm–1) of ν2, ν3, and ν6 with all nine fundamentals.
| v i | Band position | B3LYP-D3(BJ)/aVTZ VPT2 |
||
| x 2i | x 3i | x 6i | ||
| 1 | 3533 | –3.5 | –1.1 | –0.9 |
| 2 | 2892 | –61.9 | –13.4 | –2.3 |
| 3 | 1779 | –13.4 | –9.3 | –4.1 |
| 4 | 1374 | –20.4 | –0.3 | –6.2 |
| 5 | 1219 | –6.1 | +2.8 | –14.3 |
| 6 | 1089 | –2.3 | –4.1 | –6.2 |
| 7 | 622 | +0.4 | –6.2 | –3.7 |
| 8 | 1031 | –17.1 | –5.4 | –3.7 |
| 9 | 643 | –2.8 | –0.4 | –5.6 |