Vibration-rotation bands of allene

The vibrational absorption spectrum of allene has been reinvestigated using a new grating spectrometer of high resolving power. The rotational structure of many of the bands has been measured and discussed in relation to the geometrical structure of the molecule. The perpendicular-type bands associated with absorption of the fundamental frequencies of degenerate oscillations show features of particular interest. Two of these bands provide an elegant example of a type of Coriolis perturbation originally predicated by Nielsen, and which results in an unusual arrangement of the Q branches in each band.