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

Compare vibrational frequencies for two calculations for C2H5 (Ethyl 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 A' A'   2978 3058 -79.9 0.974   1.051 1.052 -0.000 1.000   19.08 12.82 6.26 1.488
2 A' A'   2901 2972 -71.1 0.976   1.080 1.086 -0.006 0.995   41.85 21.87 19.98 1.914
3 A' A'   2840 2892 -52.5 0.982   1.053 1.048 0.005 1.005   40.16 20.68 19.48 1.942
4 A' A'   1465 1464 1.0 1.001   1.067 1.107 -0.040 0.964   3.46 3.61 -0.14 0.960
5 A' A'   1445 1450 -4.8 0.997   1.171 1.124 0.047 1.042   1.82 2.66 -0.85 0.682
6 A' A'   1395 1386 9.3 1.007   1.188 1.207 -0.019 0.985   0.00 1.40 -1.40 0.001
7 A' A'   1000 1045 -44.8 0.957   2.776 3.156 -0.381 0.879   0.45 0.06 0.40 8.078
8 A' A'   973 971 2.5 1.003   1.416 1.323 0.093 1.070   0.04 0.38 -0.34 0.115
9 A' A'   413 437 -24.6 0.944   1.220 1.218 0.002 1.002   45.34 54.45 -9.11 0.833
10 A" A"   3066 3160 -93.9 0.970   1.119 1.119 -0.000 1.000   28.95 13.98 14.97 2.071
11 A" A"   2932 3015 -82.2 0.973   1.104 1.103 0.000 1.000   36.26 18.26 18.00 1.986
12 A" A"   1469 1469 0.1 1.000   1.039 1.038 0.001 1.001   2.91 4.61 -1.71 0.630
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.