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

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

PBEPBE/3-21G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 2209 -81 Σg 2290  
2 Σg 2018 -101 Σg 2119  
3 Σg 586 -106 Σg 692  
4 Σu 2140 -101 Σu 2241  
5 Σu 1130 -24 Σu 1154  
6 Πg 902 398 Πg 504  
7 Πg 326 63 Πg 263  
8 Πu 682 210 Πu 472  
9 Πu 111 4 Πu 107  
The calculated vibrational frequencies were scaled by 0.9535

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.