Tables 61 1 {continued) and 61 2 503 



NORMAL SERIES RELATIONS IN ATOMIC SPECTRA (continued) 



(d) The components of a term are characterized by inner quantum numbers J, and the 

 terms themselves by quantum numbers L, according to the following scheme. 



TABLE 612. — Inner Quantum Numbers 



Line-producing combinations occur only between components for which the difference 

 A J is o or ±r. The combination of two multiple terms thus gives rise to a group of lines 

 called a multiplet. 



(e) In such a group the lines for which A J = AL are the strongest (often called the 

 diagonal lines) and the line for which the J's are largest is the strongest of these. These 

 intensity relations (which have been calculated in detail) are of great practical importance. 

 The successive separations of the components of a multiple term are normally proportional 

 to the larger value of J involved; (Lande's interval rule). The factor of proportionality 

 is different for different terms. It increases rapidly with the atomic number Z, and is 

 roughly proportional to Z 2 for similar elements, such as Ca, Sr, Ba. The character of the 

 Zeeman effect for any line is completely defined by the numbers R, L, J, for the two levels 

 involved. It is usually possible to work backward from a completely resolved Zeeman 

 pattern and find the nature of the terms involved — a great aid in the analysis of complex 

 spectra. 



(f) In the simplest spectra, all the terms for which L is even or odd are themselves 

 even or odd, so that AL = ± 1 for all lines. But in complex spectra all values of L appear 

 among both odd and even terms, and transitions for which AL = also give strong 

 multiplets. Transitions for which AL = ± 2, and a few for which it is ± 3, are known, 

 but usually give faint lines. Lines for AJ — ± 2 are however extremely rare (except in 

 strong magnetic fields). 



(g) In arc spectra — that is, the spectra of neutral atoms — the multiplicities of the 

 various systems are always even if the atomic number is odd, and vice versa, so that odd 

 and even multiplicities alternate. The spectrum of a singly ionized atom is similar in 

 general structure to that of the element of next preceding atomic number ; of a doubly 

 ionized atom to the element preceding this, and so on (the displacement lazv). In con- 

 sequence the alternation of odd and even multiplicities is found for successive ionizations 

 of the same element. 



(h) The maximum multiplicity in arc spectra is 2 for elements in which there is but 

 one electron outside "completed shells" (Li, Na, K, Rb, Cs ; also B, Al, Ga, In, Tl). 

 From these elements it increases by steps of a unit till the " shell " is half completed and 

 then diminishes in the same way — the maximum values being 5 for O, S, Se (Te) and 8 

 for Mn, (Ma) Re. (Parentheses denote predictions for incompletely analyzed spectra.) 

 In the rare earths it probably rises to II. When the maximum multiplicity increases with 



Smithsonian Tables 



