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Using PM6, the second vibrational mode of formaldehyde, a B1, occurs at 1155cm-1. This corresponds to a vibrational period of 1/(1155x3x1010) seconds, or 28.9x10-15 s, or 28.9 femtoseconds. Like vibration 1, this is a very symmetric vibration in that the two halves of the potential curve have the same shape. In this simulation, each frame represents 0.2 fs, and the display is 50 frames per second, so each second represents 10fs. If, using a stopwatch, you time all 10 complete vibrations, it'll come to about 29 seconds, therefore the simulation represents a total of 290fs. From this it follows that each vibration takes about 29.0 fs and has a frequency of 1/(3x1010x29.0x10-15) cm-1 or 1149 cm-1 in accordance with the results of the vibrational calculation. |
Data set used by MOPAC:
irc=2 drc cycles=942 t-priority=0.2 Formaldehyde O 0.00000000 +0 0.0000000 +0 0.0000000 +0 -0.4225 C 1.21074828 +1 0.0000000 +0 0.0000000 +0 1 0 0 0.2366 H 1.09713884 +1 122.0336155 +1 0.0000000 +0 2 1 0 0.0929 H 1.09712655 +1 122.0249758 +1 180.0000000 +0 2 1 3 0.0929