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Compare vibrational frequencies for two calculations for C2H3 (vinyl)


A = HF/6-31G*
B = MP2/6-31G*

scale factors=0.8985, 0.943 -4.254 1.357
  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'   3081 3147 -65.8 0.979   1.095 1.111 -0.017 0.985   3.81 1.96 1.947
2 A' A'   3030 3086 -56.0 0.982   1.109 1.108 0.001 1.001   12.07 3.95 3.059
3 A' A'   2946 2993 -46.8 0.984   1.057 1.063 -0.006 0.995   9.60 2.15 4.461
4 A' A'   1469 1753 -283.7 0.838   1.504 5.758 0.261   1.49 2.31 0.645
5 A' A'   1265 1382 -117.2 0.915   2.441 1.083 2.253   3.39 7.83 0.433
6 A' A'   1075 1057 17.8 1.017   1.471 1.507 -0.036 0.976   8.34 11.40 0.732
7 A' A'   745 726 18.4 1.025   1.053 1.054 -0.001 0.999   12.52 21.12 0.593
8 A" A"   861 1004 -142.2 0.858   1.194 1.212 -0.018 0.985   69.97 87.56 0.799
9 A" A"   795 936 -141.1 0.849   1.270 1.272 -0.002 0.999   2.47 10.54 0.234
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.