On the vibrational contributions to the partition function of acetamide

The partition function in the documentation considers torsionally excited states. 
The contributions of the small amplitude vibrations were evaluated 
in the harmonic approximation. The values were extracted from

(1) A. Belloche, A. A. Meshcheryakov, R. T. Garrod, V. V. Ilyushin, E. A. Alekseev, 
R. A. Motiyenko, L. Margulès, H. S. P. Müller, and K. M. Menten
Astron. Astrophys. 601 (2017) A49
doi: 10.1051/0004-6361/201629724

The vibrational information was taken from a quantum chemical calculation 
described in that work if no experimental data were available.

Experimental information was taken from two publications:

(2) R. A. Kydd and A. P. C. Dunham,
J. Mol. Struct. 69 (1980) 79-88;
doi: 10.1016/0022-2860(80)85266-5

(3) W. Kutzelnigg and R. Mecke, 
Spectrochim. Acta 18 (1962) 549-560;
doi: 10.1016/S0371-1951(62)80165-9


 330   2.47352
 320   2.33626
 310   2.20925
 300   2.09175
 290   1.98311
 280   1.88269
 270   1.78994
 260   1.70434
 250   1.62543
 240   1.55275
 230   1.48594
 220   1.42463
 210   1.36849
 200   1.31725
 190   1.27064
 180   1.22844
 170   1.19042
 160   1.15642
 150   1.12626
 140   1.09979
 130   1.07686
 120   1.05734
 110   1.04108
 100   1.02792
  90   1.01769
  80   1.01017
  70   1.00508
  60   1.00205
  50   1.00058
  40   1.00009
  30   1.00000
  20   1.00000
  10   1.00000