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

Compare vibrational frequencies in CCCBDB for C4H2 (Diacetylene)

BLYP/6-31G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 3388 95 Σg+ 3293  
2 Σg 2198 14 Σg+ 2184  
3 Σg 903 29 Σg+ 874  
4 Σu 3391 62 Σu+ 3329  
5 Σu 2034 14 Σu+ 2020  
6 Πg 670 43 Πg 627  
7 Πg 535 53 Πg 482  
8 Πu 487 -143 Πu 630  
9 Πu 264 33 Πu 231  
The calculated vibrational frequencies were scaled by 0.9919

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.