Physics. — "On the Excitation and Ionization Potentials of Neon and 

 Argon''. Bj G. Hkrtz. (Commniiicated by Prof. P. Ehrenfest). 



(Communicated at the meeting of May 27, 1922) 



If is known that rare gases and metallic vapours behave in a 

 very simple way on collision with slow electrons. Then there can 

 be exchange of energy between electrons and atoms only in one 

 way, viz. that in which the transferred energy is used to bring the 

 colliding atom into a higher quantum condition. Hence on collision 

 with the atoms the electrons can transfer only very definite energy 

 quanta to them, which according to Bohr's theory, are in direct 

 connection with the series-spectrum of the atom. For a great many 

 metallic vapours this transition of energy in quanta has already 

 been investigated and the relation to the optic speclia has been 

 shown. Of the rare gases accurate measurements have only been 

 carried out for helium '), on the ground of which Fkanck succeeded 

 in making the system of the series-spectra of helium complete, and 

 in showing the connection between the ortho-helium and the par- 

 helium spectrum. Several observations have, indeed, been made for 

 neon and argon *), but the results are inaccurate for the greater 

 part, and partly in conflict witli each other. Besides in the great 

 sensitiveness of noble gases to traces of impurities, the excitation 

 and ionization potentials of which lie nearly always below that of 

 the rare gas, the cause of these conflicting results seems to lie 

 chiefly in this that the efiiciency of the unelastic collisions in the rare 

 gases is much smaller than in the metallic vapours, so that the 

 methods which lead to good results for the latter, cannot be applied 

 here. In order to attain reliable results, it seemed, therefore, neces- 

 sai-y to me, to refine the methods for the investigation of the quantum 



1) F. Horton and A. G. Da vies, Proc. Roy. Soc. London (A) 95, 408, 1919. 

 J. Franck and P. Knipping, Zeitschr. f. Physik, 1, 320, 1920. 

 K. T. CoMPTON, Phil. Mag. 40, 553, 1920. 



*) F. Horton and A. C. Davies, Proc. Roy. Soc. London, (A), 97, 1,1920 and 

 98, 124. 1920. 



G. Stead and P. S. Gosling, Phil. Mag. 40, 413, 1920. 

 H. G. Rentsghler, Phys. Rev. 14, 503, 1913. 

 G. Déjardin, C.R. 172, 1347, 1921. 



