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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 3389 96 Σg+ 3293  
2 Σg 2198 14 Σg+ 2184  
3 Σg 903 29 Σg+ 874  
4 Σu 3391 62 Σu+ 3329  
5 Σu 2033 13 Σu+ 2020  
6 Πg 683 56 Πg 627  
7 Πg 555 73 Πg 482  
8 Πu 522 -108 Πu 630  
9 Πu 265 34 Πu 231  
The calculated vibrational frequencies were scaled by 0.9923

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.