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IV.C.1. (XIII.D.1.)

Compare vibrational frequencies in CCCBDB for C4H4 (cyclobutadiene)

MP2=FULL/3-21G

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Ag 3150 10 Ag 3140 CH str
2 Ag 1453 -225 Ag 1678 C=C str
3 Ag 1072 13 Ag 1059 CH def
4 Ag 866 -123 Ag 989 CH def
5 Au 707        
6 Au 477        
7 B1g 791        
8 B1u 3134 10 B1u 3124 CH str
9 B1u 1442 -85 B1u 1527 C=C str
10 B1u 1029 1 B1u 1028 CH def
11 B2g 527 -4 B2g 531 CH OPLA
12 B2u 3114 9 B2u 3105 CH str
13 B2u 1227 -17 B2u 1244 CH def
14 B2u 576 -143 B2u 719 ring def
15 B3g 3102 9 B3g 3093 CH str
16 B3g 1166        
17 B3g 848        
18 B3u 567 -9 B3u 576 CH OPLA
The calculated vibrational frequencies were scaled by 0.9548

See section XIII.C.3 List or set vibrational scaling factors to change the scale factors used here.
See section III.B.3.c Calculate a vibrational scaling factor for a set of molecules to determine the least squares best scaling factor.
See section III.B.3.b List of vibrational scaling factors and their uncertainties for information on where the above scaling factor is from.