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

QCISD/6-31+G**

18 11 26 13 55
Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency Scaled
Frequency
Harm.
diff
Fund.
diff
Symmetry Harmonic
Frequency
Fundamental
Frequency
Comment
1 Σg 2434 2301   11 Σg   2290  
2 Σg 2206 2086   -33 Σg   2119  
3 Σg 602 569   -123 Σg   692  
4 Σu 2339 2212   -29 Σu   2241  
5 Σu 1154 1091   -63 Σu   1154  
6 Πg 308 291   -213 Πg   504  
7 Πg 157 149   -114 Πg   263  
8 Πu 468 442   -30 Πu   472  
9 Πu 116 109   2 Πu   107  
The calculated vibrational frequencies were scaled by 0.9454

See section Calculated; Vibrations; Scale Factors; Set scaling factors to change the scale factors used here.
See section Calculated; Vibrations; Scale Factors; Calculate a scale factor to determine the least squares best scaling factor.
See section Calculated; Vibrations; Scale Factors; Scale factor uncertainty for information on where the above scaling factor is from.