Free jet absorption millimeter wave spectrum of 2,4'-dipyridyl

The free jet millimeter wave spectrum of 2,4'-dipyridyl has been investigated in the frequency range 60-78 GHz. The two pyridine rings are tilted with respect to each other by 22.7 degrees. Each rotational transition is split into two component lines due to the torsional motion connecting 4 equivalent minima. The lower of the two barriers to inversion, corresponding to the planar configuration, has been calculated to be 45 cm(-1)