| Compound | IR characteristic bands |
| ||
| ν (C=O) | ν (C-O) | ν (V=O) | ν (C-O-V) | |
| 1a (pellet) | 1588 | 1551 | 970 | 1327 |
| 1a (thin film) | 1589 | 1554 | 998 | 1328 |
| 2a (pellet) | 1594 | 1545 | 986 | 1327 |
| 2a (thin film) | 1600 | 1550 | 992 | 1328 |