AUGER DISRUPTIONS 107 



and varies somewhat with the velocity of the particle. Ionization of K 

 levels by secondary electrons is entirely negligible. The ejection of inner 

 electrons by swift charged particles — both electrons and heavy particles 

 — has been verified experimentally in the observation of characteristic 

 x-rays emitted by atoms during irradiation with these particles. 



Where a K shell of a C, N, or O atom has been ionized, an energy 

 transfer of some hundreds of electron volts to the molecule containing 

 the atom has occurred. (The exact values are 284 ev for C, 400 ev for 

 N, and 531 ev for 0.) If the molecule is moderately or very large, it 

 will retain all this energy! Creation of a 7v-shell vacancy in these very 

 light atoms is not followed by emission of an x-ray photon, as is the case 

 for a heavy atom. There ensues instead a radiationless transition in 

 which an L electron drops into the vacancy and a second L electron is 

 ejected from the atom. Thus a doubly ionized atom results. (Before 

 emitting a photon of K radiation, an atom persists in its excited state 

 for a period of the order of 10~^Z~^ sec, where Z is its atomic number. 

 For very light atoms this is so much longer than the time required for 

 radiationless transition that the latter almost always occurs first. 

 The yield of radiation from C, N, or O is certainly smaller than 1 per 

 cent.) Such a process, commonly called an Auger transition, takes place 

 within a time interval of about 10~^^ sec. It is so much faster than 

 any possible motions of atomic nuclei in the molecule that, as follows 

 from the Franck-Condon principle, the nuclei cannot respond appreci- 

 ably until after the second electron has left. Whether the ejected elec- 

 tron must be one belonging to the same atom that suffered K ionization, 

 or may originate in an atom bonded to it, is not known, and the question, 

 moreover, is not free from ambiguity. In any case the distinction is 

 not very important, for the molecular ion will have ample time for elec- 

 tronic readjustments before dissociation proceeds. It is also worthy of 

 mention that in some instances not only one but several Auger transi- 

 tions might follow a single K ionization, for very much more than suf- 

 ficient energy is available to ionize several valence electrons at or near 

 the site of the original vacancy. 



The great quantity of energy transferred to a single atom when one 

 of its inner electrons is ejected will not remain in that atom, of course — 

 except for the minor portion retained by virtue of the ionization (and 

 perhaps also excitation) of the valence shell. Where the atom is bound 

 in a large molecule, however, the energy carried away by the Auger 

 electron (s) will not escape, for such electrons dissipate their energy in 

 excitations and ionizations within a distance of less than about 10 A. 

 (Indeed, it may be proper to raise the question whether, in the case of 

 polyatomic molecules, it is valid to consider the Auger transition and 



