[ 659 ] 



LXXVIII. A Significant Exception to the Principle of 

 Selection. By Paul D. Foote, Ph.D., F. L. Mohler, 

 Ph.D., and W. F. Meggers, Ph.D.* 



[Plate XIII.] 



ACCORDING to the Rubinowicz t principle of selection, 

 the azimuthal quantum number, in any transition of 

 an electron between two stationary orbits, resulting in 

 radiation, may change by only +1, 0, or —1. 



Now, in the enhanced lines A, = 4686 and A. 3203 emitted by 

 the ionized helium atom, there appear to be certain experi- 

 mentally observed components which on the basis of the above 

 principle should not exist. Rubinowicz states that the fact 

 that these extra lines have been observed, for which the 

 change in the azimuthal quantum number is 2, obviously ± 

 may be attributed to the presence of the electrostatic field 

 exciting the radiation. 



While from a consideration of the application of the 

 quantum theory to the Stark effect, and the resulting 

 necessary introduction of a third quantizing process in the 

 mathematical analysis of the lines, Rubinowicz's explanation 

 is consistent with possible fact, it is, of course, by no means a 

 necessary deduction. On the aspherical nucleus theory of 

 Silberstein §, for example, there should be many more 

 components than would arise with the radially symmetrical 

 (i.e. spherical) nucleus assumed in the Rubinowicz theory, 

 and in the more restricted theories of Bohr and Sommerfeld. 



A most interesting extension of the quantum theory to the 

 derivation of general spectral series relations, for atoms with 

 several electrons, has been made by Sommerfeld ||,in which 

 he associates definite azimuthal quantum numbers with the 

 series terms : for example, n a =l for the ms terms, 2 for the 

 mp terms, 3 for the md terms, and 4 for the mb terms. 

 Here, again, exceptions to the principle of selection have been 

 noted and have been attributed to the presence of the 

 exciting electrostatic field, an explanation entirely satisfac- 

 tory from the mathematical standpoint, if one admits that the 

 lines would not be present in the absence of the field. 



* Oorumimicated by the Authors. Published by permission of the 

 Director, Bureau of Standards. 



t Rubinowicz, Phys. Zeit. xix. pp. 441 and 465, 1918. An application 

 of the principle of conservation of moment of momentum to the inter- 

 action of aether and matter, in addition to the postulates originally 

 proposed by Bohr. 



% Loc. cit. p. 466, " handgreiflich." 



§ Silberstein, Proc. Roy. Soc. xcviii, p. 1, 1920. 



II Summarized in several chapters of ' Atombau.' 



2 U 2 



