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

Compare vibrational frequencies in CCCBDB for C2H2 (Acetylene)

PBEPBEultrafine/6-31G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 3412 38 Σg 3374  
2 Σg 1994 20 Σg 1974  
3 Σu 3316 27 Σu 3289  
4 Πg 444 -168 Πg 612  
5 Πg 445 -167 Πg 612  
7 Πu 729 -1 Πu 730  
The calculated vibrational frequencies were scaled by 0.9835

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.