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

Compare vibrational frequencies in CCCBDB for C4H2 (Diacetylene)

B2PLYP/6-31G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 3334 41 Σg+ 3293  
2 Σg 2148 -36 Σg+ 2184  
3 Σg 871 -3 Σg+ 874  
4 Σu 3335 6 Σu+ 3329  
5 Σu 1982 -38 Σu+ 2020  
6 Πg 596 -31 Πg 627  
7 Πg 596 -31 Πg 627  
8 Πg 531 49 Πg 482  
9 Πg 531 49 Πg 482  
10 Πu 518 -112 Πu 630  
11 Πu 518 -112 Πu 630  
12 Πu 246 15 Πu 231  
13 Πu 246 15 Πu 231  
The calculated vibrational frequencies were scaled by 0.9492

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.