text: Molecular fly-by collisions take little time, something like 10 s. 
  Optical transition of collisional complexes of molecules generate spectral 
  "lines" that are very broad - roughly five orders of magnitude broader 
  than the most familiar "ordinary" spectral lines (Heisenberg's uncertainty 
  relation). The resulting spectral "lines" usually strongly 
  overlap so that collision-induced spectral bands typically appear as continua 
  (as opposed to the bands of often discernible lines of ordinary molecules).
  Collision-induced spectra appear at the frequencies of the rotovibrational and 
  electronic transition bands of the unperturbed molecules, and also at sums and 
  differences of such transition frequencies: simultaneous transitions in two (or 
  more) interacting molecules are well known to generate optical transitions of
  molecular complexes.