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III.G.7. (XIII.B.3.) (XIII.D.5.)

Compare vibrational frequencies for two calculations for C2H (Ethynyl radical)

A = HF/6-31G*

B = MP2/6-31G*

scale factors=0.8985, 0.943
  symmetry   frequency (cm-1)   reduced mass (amu)   IR Intensity (km mol-1)
mode number A B   A B diff. ratio   A B diff. ratio   A B diff. ratio
1 Σ Σ   3254 3395 -140.7 0.959   1.125         43.30 53.21 -9.91 0.814
2 Σ Σ   1666 2342 -676.7 0.711   6.653         1.59 8.92 -7.33 0.178
3 Π Π   501 772 -271.0 0.649   1.328         31.90 15.54 16.36 2.053
4 Π Π   501 772 -271.0 0.649   1.328         31.90 15.54 16.36 2.053
scaled by     0.8985 0.943

See section III.C.1 List or set vibrational scaling factors to change the scale factors used here.
See section III.C.2 Calculate a vibrational scaling factor for a given set of molecules to determine the least squares best scaling factor.