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

Compare vibrational frequencies in CCCBDB for C4H2 (Diacetylene)

MP2/CEP-121G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 3316 23 Σg+ 3293  
2 Σg 2066 -118 Σg+ 2184  
3 Σg 845 -29 Σg+ 874  
4 Σu 3317 -12 Σu+ 3329  
5 Σu 1893 -127 Σu+ 2020  
6 Πg 1132 505 Πg 627  
7 Πg 656 174 Πg 482  
8 Πu 788 158 Πu 630  
9 Πu 311 80 Πu 231  
The calculated vibrational frequencies were scaled by 0.9528

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.