Alternative explanation of the nature of line clumps
  It is assumed, that the clumps of lines do not connected with states mixing and IVR, but they are the result of breaking (destruction) of the process of averaging of momentum of inertia of molecules during the vibration motion of atoms. Rough estimates of the widths of clumps of lines in absorption spectra of some acetylenic derivatives were made with this model. Obtained results are in a satisfactory agreement with the available experimental data. This idea allows also in principle to explain the origin of intensive wings of lines, the existence of which was discussed earlier. 
V.A. Kuz'menko