PAPERS OX CHEMISTRY AND PHYSICS 279 



THE IXFRA-RED ABSORPTIOX OF SOME OXIDES 

 OF XITROGEX 



B. J. Spexce. Xorthwesteex Uxn'ERsrrY 



The follo\viug- is intended merely as a preliminary re- 

 port of work taken np in an attempt to add to the data 

 bearing npon the considerable theory already developed 

 for the infra-red absorption of gases made np of simple 

 molecnles. The theory in the case of a simple diatomic 

 gas assnmes that the molecnle is made np of two atomic 

 nnclei separated by only a short distance. These nnclei 

 are held together by a ring of electrons rotating about an 

 axis joining the two nnclei and between them. According 

 to the qnantiim theory it is possible for a molecnle to 

 rotate abont an axis at right angles to the line joining 

 the nnclei with delinite bnt different velocities. If the 

 moment of inertia does not change, these different veloci- 

 ties of rotation will manifest themselves as simple ab- 

 sorption bands in the far iiifra-red region. If, on the 

 other hand, isotopes of one of the atomic nnclei exist, 

 there will be different moments of inertia of the mole- 

 cnle. The different moments of inertia will not differ 

 greatly and instead of a series of simple bands, we shall 

 find a series of more complex bands, for example, trip- 

 lets, where two isotopes of one of the nnclei exist. 



If the nnclei vibrate along the line joining their cen- 

 ters with a simple harmonic motion, the vibration will 

 manifest itself as an absorption band in the near infra- 

 red region. This freqnency of vibration may combine 

 with a rotation freqnency to produce a series of bands 

 in the region of the vibration freqnency. If the vibra- 

 tion freqnency is not simple harmonic on account of large 

 nnclear displacements, such a vibration will give rise 

 to harmonics whose frequencies are approximate mnlti- 

 ples of a fundamental frequency. These in turn may 

 combine with the rotation frequencies to produce the 

 complicated system of bands in the region of the har- 

 monic frequencies. In short, there should be rotation 

 frequencies, vibration frequencies, harmonic frequencies, 

 and combination frequencies. These, however, need not 



