1010 Drs. Foote, Meggers, and Mohler on Excitation of 



energy level. The outermost stable orbit 1*5 S contains the 

 two valence electrons, and the arc spectrum is produced by 

 one of these returning toward equilibrium following a dis- 

 placement. Several of the more fundamental lines are 

 shown on this plot. For example, a displacement of one 

 electron to the left from 1*5 S to 2p 2 requires an amount of 

 work represented by 2' 65 volts. On returning to equilibrium 

 this amount of energy is radiated in the line \4573. The 

 arrow-head shows the direction and end of the displacement 

 in each case. 



Fig. 3 represents the enhanced spectrum and X-rays in a 

 similar manner. It will be noted that one of the valence 

 electrons is absent, which greatly alters the values of the 

 different energy levels. 



Fiff. 3. 



I Radiation - 



■* L a 46.9 Volts- 



-TVo-fold Ionization 14.37 V«lt$ 

 -5impl« Enhanced 5f>ectrt»m 

 3 S 6 1.56 



15 S 



1,1 M I II f 



4g 



32 



*2 



/la^nesiora 



J I 



4.6- 4.1 43 43 



Log Wave Number 



5.1 5.3 SA 



Schematic drawing representing- lines of the enhanced spectrum 

 and X-rays. 



If the enhanced spectrum arises in an arc at 14*97 volts, 

 the electronic impact must occur with an atom already 

 simply ionized. That is, the atom before it recovers from an 

 impact of 7*61 volts, resulting in simple ionization, must be 

 subjected to a second impact of 14*97 volts, resulting in 

 double ionization. Otherwise the enhanced spectrum would 

 require a voltage equivalent to 1*5 (5 + 1*5 S or 14*97 + 7 '61 

 = 22*58 volts for its excitation. No marked change in the 

 spectrum could be detected at this latter value, indicating 

 that, at least with the current and vapour densities employed 

 in this work, two successive collisions, each resulting in the 

 ejection of an electron, were more probable than a single 

 collision resulting in the ejection of two electrons. That 

 the phenomenon of successive collision is, in general, an 



