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

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

MP2/3-21G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 2181 -109 Σg 2290  
2 Σg 1906 -213 Σg 2119  
3 Σg 559 -133 Σg 692  
4 Σu 2022 -219 Σu 2241  
5 Σu 1064 -90 Σu 1154  
6 Πg 729 225 Πg 504  
7 Πg 269 6 Πg 263  
8 Πu 624 152 Πu 472  
9 Πu 106 -1 Πu 107  
The calculated vibrational frequencies were scaled by 0.9513

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.