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

Compare vibrational frequencies in CCCBDB for C4N2 (2-Butynedinitrile)

MP2/6-31G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 2133 -157 Σg 2290  
2 Σg 1932 -187 Σg 2119  
3 Σg 573 -119 Σg 692  
4 Σu 2048 -193 Σu 2241  
5 Σu 1102 -52 Σu 1154  
6 Πg 478 -26 Πg 504  
7 Πg 252 -11 Πg 263  
8 Πu 471 -1 Πu 472  
9 Πu 108 1 Πu 107  
The calculated vibrational frequencies were scaled by 0.943

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.