Table 5. Calculated and Experimental Fundamental Frequencies of Cyclobutadiene (Unit in cm–1)a.
| no. | sym. | exp. | Eckart calc. | SD calc. | err. (%) | active | action |
|---|---|---|---|---|---|---|---|
| 1 | b2g | 53183 | 505.7 | 505.3 | –4.8 | Raman | CH OPLA deform |
| 2 | b3u | 56986 | 556.5 | 556.9 | –2.1 | IR | CH OPLA |
| 3 | b2u | 71986 | 709.9 | 710.0 | –1.4 | IR | ring deform |
| 4 | b3g | 72383 | 827.8 | 827.6 | 14.5 | Raman | ring deform |
| 5 | ag | 98983 | 935.0 | 935.1 | –5.5 | Raman | CH deform |
| 6 | b1u | 102886 | 1002.1 | 1002.2 | –2.5 | IR | CH deform |
| 7 | ag | 105983 | 1093.7 | 1093.6 | 3.2 | Raman | CH deform |
| 8 | b3g | 1121.9 | 1121.8 | Raman | C–C stretch | ||
| 9 | b2u | 124286 | 1198.8 | 1198.8 | –3.5 | IR | C–H deform |
| 10 | ag | 167883 | 1611.0 | 1611.1 | –4.0 | Raman | C=C stretch |
| 11 | b3g | 309383 | 3121.4 | 3121.3 | 0.9 | Raman | CH stretch |
| 12 | b2u | 310584,86 | 3139.3 | 3139.3 | 1.0 | IR | CH stretch |
| 13 | b1u | 312485,86 | 3159.7 | 3159.9 | 1.1 | IR | CH stretch |
| 14 | ag | 314083 | 3172.6 | 3172.7 | 1.0 | Raman | CH stretch |
a
The data in the SD calc. column are calculated using the second derivative of the MD trajectory.