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

Compare vibrational frequencies for two calculations for CH3CN- (acetonitrile 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 A1 A1   2908 2947 -39.8 0.987   1.034 1.034 -0.000 1.000   4.88 2.23 2.65 2.188
2 A1 A1   2357 2103 254.0 1.121   12.619 12.390 0.230 1.019   13.08 0.16 12.92 82.849
3 A1 A1   1405 1387 18.0 1.013   1.228 1.234 -0.006 0.995   0.64 3.34 -2.69 0.193
4 A1 A1   875 890 -16.0 0.982   4.638 4.574 0.064 1.014   8.21 1.75 6.46 4.703
5 E E   2980 3037 -56.6 0.981   1.105 1.104 0.001 1.001   3.94 0.78 3.16 5.033
6 E E   1453 1450 2.8 1.002   1.040 1.042 -0.002 0.998   9.23 10.90 -1.66 0.847
7 E E   1055 1031 24.5 1.024   1.438 1.395 0.043 1.031   1.54 2.52 -0.98 0.609
8 E E   382 334 48.1 1.144   3.806 4.106 -0.301 0.927   1.63 0.51 1.12 3.174
9 A" E   2922 1031 1891.2 2.835   1.092 1.395 -0.303 0.783   93.72 2.52 91.20 37.196
10 A" E   1279 1031 248.0 1.241   1.060 1.395 -0.335 0.760   39.91 2.52 37.39 15.839
11 A" E   662 334 327.9 1.982   1.868 4.106 -2.239 0.455   113.14 0.51 112.63 220.418
12 A" E   323 334 -10.8 0.968   2.295 4.106 -1.811 0.559   4.05 0.51 3.54 7.897
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.