ARC SPECTRA AND IONIZATION POTENTIALS IN 

 DISSOCIATED GASES. 



By K. T. COMPTON, 



(Read April 21, 1922) 



The great complexity of spectra is due, in part, to the fact that the 

 molecules may exist in various states of association, dissociation, and 

 ionization, each type of molecule or atom giving rise to its own char- 

 acteristic spectrum. A discovery of the exact state of the atom or 

 molecule giving rise to each part of the spectrum of a substance is 

 of great importance as regards both the theory of spectral emission 

 and the theory of atomic and molecular structure. At the Palmer 

 Physical Laboratory this problem is being attacked from three dif- 

 ferent angles. This paper presents some discoveries made by two of 

 these methods and discusses their significance. 



Hydrogen. 

 Bohr's theory is believed satisfactorily to account for the known 

 properties of hydrogen atoms. Hydrogen ordinarily exists, however, 

 in the form of diatomic molecules, whose properties have not been 

 adequately explained by any hypothesis of molecular structure yet 

 proposed. Those properties of the hydrogen atom which Bohr's 

 theory explains are the series spectrum and the energy required to 

 produce radiation or to ionize the atoms, commonly expressed as 

 radiating and ionizing potentials, respectively. Other radiating and 

 ionizing potentials and another type of spectrum are believed to be 

 due to hydrogen molecules. In no case has there been direct and 

 definite evidence as to which type of spectrum is due to the atom and 

 which to the molecule, although sufficient indirect evidence is at hand 

 to ascribe the series spectrum to the atom and the secondary spectrum 

 to the molecule with considerable certainty. There has been no 

 experimental evidence at all as to which entity to ascribe each radi- 

 ating or ionizing potential observed in hydrogen. The assignment of 



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