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Compare vibrational frequencies in CCCBDB for CH3NO2 (Methane, nitro-)

B97D3/3-21G

18 11 26 13 55
Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency Scaled
Frequency
Harm.
diff
Fund.
diff
Symmetry Harmonic
Frequency
Fundamental
Frequency
Comment
1 A' 3144 3091   46 A'   3045  
2 A' 3046 2994   20 A'   2974  
3 A' 1506 1480   83 A'   1397  
4 A' 1382 1358   -76 A'   1434  
5 A' 1146 1126   -254 A'   1380  
6 A' 1094 1075   -56 A'   1131  
7 A' 787 773   -145 A'   918  
8 A' 572 562   -95 A'   657  
9 A' 517 508   -95 A'   603  
10 A" 3178 3124   44 A"   3080  
11 A" 1505 1479   -104 A"   1583  
12 A" 1336 1313   -97 A"   1410  
13 A" 1045 1028   -68 A"   1096  
14 A" 416 409   -66 A"   475  
15 A" 46i 45i    A"     internal rotation, almost free rotor
The calculated vibrational frequencies were scaled by 0.983
Nitromethane is essentially a free rotor. The calculations produce one of three conformations: 1) the NO2 plane perpendicular to a C-H bond, Cs symmetry; 2) The NO2 plane lined up with a C-H bond, Cs symmetry; 3) The NO2 plane at some small angle away from a C-H bond (C1 symmetry). Note that conformation 1 has 9 A' modes and 6 A" modes, conformation 2 has 10 A' modes and 5 A" modes, and conformation 3 has 15 A modes.

See section Calculated; Vibrations; Scale Factors; Set scaling factors to change the scale factors used here.
See section Calculated; Vibrations; Scale Factors; Calculate a scale factor to determine the least squares best scaling factor.
See section Calculated; Vibrations; Scale Factors; Scale factor uncertainty for information on where the above scaling factor is from.