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XXI. On the Probability of Ionization and Radiation of 

 Gas Molecules due to Collision with Electrons, By K. F. 

 Nesturch*. 



AS recently shown by Franck and Hertz f, the electrons 

 in electropositive gases (He, Ne, Ar, also mercury 

 vapour), set in motion by the action of an electric field, 

 collide elastically with neutral gas molecules. Consequently 

 when passing a fall of potential, the electrons accumulate 

 kinetic energy independently of the number of collisions on 

 their way, i. e, independently of the pressure of the gas. 



When an electron has obtained a certain amount of 

 energy, its next collision with a gas molecule is an inelastic 

 one; it loses its energy, which is then transferred to the 

 molecule. The amount of energy, possessed by the electron 

 at the moment of the inelastic collision, is a characteristic 

 quantity of the gas, the corresponding fall of potential being 

 the "ionizing potential " of the latter. 



Franck and Hertz have brought forward numerous argu- 

 ments! in favour of the view that the energy, which an 

 electron loses by this inelastic shock, can either ionize the 

 molecule or force it to emit radiation of a definite wave- 

 length, but that both processes cannot occur simultaneously. 



To this it may be added that according to the model of the 

 atom, recently designed by Dr. Bohr §, the possibility of 

 such transformation of energy is very obvious in both cases. 



It is possible to suppose then that the ratio of probabilities 

 of ionization and radiation is a characteristic property of the 

 gas. In this article the author will attempt to indicate a 

 method for a rough determination of the numerical values of 

 the above probabilities for electropositive gases only. 



In the first place a formula is to be given for the value of the 

 electric current between the two plane electrodes in a homo- 

 geneous field, the gradient of potential being X. The two 

 following assumptions are made for the sake of simplicity. 

 1. The " ionizing distance," which the electron must pass 

 before it has gained the amount of energy sufficient to expe- 

 rience an inelastic shock, must be great as compared with 

 the mean free path of the electrons. 2. £, the distance 

 between the plates, must be an exact multiple of the ionizing 



* Communicated by the Author, having been read before the Eussian 

 Physico-Chemical Society at the meeting of 22 December, 1914. 

 t Verh. d. D. Phys. Ges. xv. (1913) ; xvi. p. 457 (1914). 

 % L. c. and Verh. d. D. Phys. Ges. xvi. p. 512 (1914). 

 § Phil. Mag.xxvi. p. 1 (1913). 



