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).