NO. 5 HYDROGEN CYANIDE BRACKETT AND LIDDEL 7 



INVESTIGATION OF VAPOR 



The absorption spectrum has been obtained of saturated vapor at 

 22.5 °C., with a 30 cm. length of cell. The three bands observed in 

 the gas absorption, interpreted as 2i'a, ^v^, and 2vi + v2 all show clearly 

 a doublet structure. In the stronger bands, 2vi and 3vi shown in 

 figure 5, separations of maxima are obtained of 47 ±2 cm."'^ and 

 50±2 cm.~^, which yield moments of inertia 2i±2Xio~*° g. cm.', 

 and i8±2XiO""*° g. cm.- respectively. This is consistent, within the 

 order of the accuracy of the work, with the more accurate value ob- 

 tained by Badger. The combination band is too weak to obtain 

 separation values of significance. On the basis of this conclusive 

 identification of fundamentals, the clearly doublet character of the 

 gas absorption implying the absence of a Q branch, and the approxi- 



103^1 I.0ZB5 



'>'A/^^WW^^' 



1.3BCZ 



I.5Z&0 I'.ssei 



Fig. 5. — Energy curves showing absorption spectrum of 30 cm. Saturated 

 HCN vapor. Slit widtli approx. 9A. 



mate values of moments of inertia, we had independently come to the 

 same conclusions regarding the arrangement of atoms, the approxi- 

 mate separations, and the probable modes of vibration before the 

 publication of the work of Badger and Binder. 



The position of the 2i'i and 3i'i bands, however, is not consistent 

 with the formula 



Assuming the formula 



j'=i //(rjji — n"oj|j.r 



our values indicate a variation in x. This is evident from table 2, 

 where the values of Ai'o or 2wo.r have successive values 59, 107, 

 and 133, indicating values of wo.r varying from 30 to 67. as against 

 Badger's value of 43.7 based only upon I'l and 4^1. Third ditlerences 



