qo4 Tables 611 (continued) and 613 



NORMAL SERIES RELATIONS IN ATOMIC SPECTRA (continued) 



increasing atomic number the spectroscopic terms have the components with small 

 J-values the lowest. Beyond the maximum they are "inverted" with the large J's low. 

 The higher the maximum multiplicity the greater, generally speaking, is the complexity 

 of the spectrum. The terms of lowest energy are even in all arc spectra except those of 

 B, N, F, and their homologues, and of some of the rare earths. 



(i) Inter-system combinations between terms of different multiplicities are common 

 when AR=2, and a few are known for which AR = 4. They are faint for elements of 

 small atomic number, but often strong when this is large. Deviations from the interval 

 and intensity rules, and the usual rules for the Zeeman effect, also become great in this 

 case. In extreme instances classification by term-types is hardly practicable, though parity 

 and inner-quantum number remain definite. 



(j) Arc lines originating in the lowest energy-level in the atom are strong at low 

 temperatures, and usually easily reversed, and are strengthened in the sun-spot spectrum ; 

 while those arising from high levels do not reverse, are produced only at higher tempera- 

 tures, and are little affected, or even weakened, in the spots. The gradation of these 

 properties follows the energy-levels so closely that the temperature classification of the 

 lines ranks with the frequency-differences and the Zeeman effect as a fundamental guide 

 in the interpretation of many-lined spectra. 



The raies ultimcs, which are the last to disappear when the quantity of the element is 

 diminished, are strong lines arising from the lowest level (or occasionally the next). 



Resonance lines are those corresponding to the transition from the lowest level to the 

 next lowest with which it can combine. Intersystem combinations, which are usually faint 

 in the arc and spark, very rarely appear as raies ultimcs, although they are often very 

 strong in the furnace, and important resonance lines. 



In spark spectra, lines arising from the lowest levels are strong in the arc, sometimes 

 appear in the furnace, and tend to reverse in the spark, while those from high levels are 

 faint in the arc (if present) and are usually diffuse in the spark. 



TABLE 613. — Spectroscopic Notation 



Until recently great diversity has prevailed, but an informal committee of American 

 spectroscopists, after extensive correspondence with a large number of workers here and 

 abroad, have suggested a notation 1 which has been generally adopted. 



The successive spectra of an element are denoted by Roman numberals, e. g., Ti I, Ti II, 

 Ti III for the spectra of neutral, singly, and doubly ionized titanium. (Lines of Rb IX 

 have been identified.) 



The type of term is denoted by letters, corresponding to the quantum numbers L of 

 Hund's theory as follows : 



(Values of L greater than 6 have not yet been met with, but are anticipated among the 

 rare earths.) 



The multiplicity is denoted by a superscript at the left i, 2 .... for singlet, doublet terms. 

 The inner quantum number is used as a subscript at the right, and the parity indicated by 

 superscript ° at the right for odd terms . . . . e. g., 4 P 2 ;° read "quartet P odd 2-i ". 



1 Phys. Rev., 33, 900, 1929. 

 Smithsonian Tables 



