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

Compare vibrational frequencies for two calculations for C2H- (Ethynyl anion)

A = HF/6-31G*

B = MP2FC/6-31G*

  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   2079 2342 -263.4 0.888   4.617         119.67 8.92 110.75 13.422
3 Π Π   1013 786 226.7 1.288   1.347 1.339 0.008 1.006   538.73 267.37 271.36 2.015
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.