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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 2188 -102 Σg 2290  
2 Σg 1912 -207 Σg 2119  
3 Σg 560 -132 Σg 692  
4 Σu 2028 -213 Σu 2241  
5 Σu 1068 -86 Σu 1154  
6 Πg 731 227 Πg 504  
7 Πg 270 7 Πg 263  
8 Πu 626 154 Πu 472  
9 Πu 106 -1 Πu 107  
The calculated vibrational frequencies were scaled by 0.9545

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.