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

Compare vibrational frequencies in CCCBDB for C2H2 (Acetylene)

PBEPBE/6-31G(2df,p)

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 3448 74 Σg 3374  
2 Σg 1997 23 Σg 1974  
3 Σu 3350 61 Σu 3289  
4 Πg 480 -132 Πg 612  
5 Πu 754 24 Πu 730  
The calculated vibrational frequencies were scaled by 0.9897

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.