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

Compare vibrational frequencies in CCCBDB for C4H2 (Diacetylene)

BLYP/6-31G(2df,p)

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 3415 122 Σg+ 3293  
2 Σg 2214 30 Σg+ 2184  
3 Σg 902 28 Σg+ 874  
4 Σu 3417 88 Σu+ 3329  
5 Σu 2040 20 Σu+ 2020  
6 Πg 563 -64 Πg 627  
7 Πg 509 27 Πg 482  
8 Πu 516 -114 Πu 630  
9 Πu 234 3 Πu 231  
The calculated vibrational frequencies were scaled by 0.9945

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.