PAPERS OX CHEMISTRY AND PHYSICS 129 



the stationary states of rotation and vibration respective- 



ly- 



The interpretation of the above expression is interest- 

 ing. When the molecule is in the state characterized by 

 the quantum numbers n = m = 0, it has no energy of vi- 

 bration and of rotation. When a change occurs during 

 absorption of energy such that n = m = 1, the frequency 

 of the absorbed radiation is given by 



h. 



f = to + 



So far this so called zero branch of the curve has never 

 been observed, as far as the writer is aware. If the 

 molecule is in the stationary state characterized by 

 n = 0, and m = 1, then a transition to n = 1, and m = 2 

 gives rise to an absorbed radiation of frequency 



h h 



f = f o + ± 



811*1 4-rI 

 This expression indicates two bands, one on each side of 

 the above zero branch. If now we allow the change from 

 n = to n = 1, and m = 2 to m = 3, and so on, we have 

 a series of equidistant bands which approximate the ex- 

 perimental values fairly well. Experimentally these 

 bands are not equidistant. The above theory was de- 

 veloped assuming an independence of m and n, or that 

 the moment of inertia of the molecule is independent of 

 the angular velocity. By making the necessary modifi- 

 cations with this point in mind an extremely satisfactory 

 theory is developed which accounts for the facts very 

 well. 



The above theory was developed for the diatomic mole- 

 cule. Xo theory exists for the polyatomic molecule. 

 However, double branched absorption bands with the fine 

 structure have been observed for polyatomic molecules. 

 Their characteristics are, in the main, similar to those of 

 the diatomic molecule. 



In an investigation to bring to light other examples 

 of these double branched absorption bands it was found 

 that ammonia gas showed a serrated double band with a 

 zero branch at 30,000 A. U. The investigation was car- 

 ried on with an infra-red grating spectrometer, using a 



