Millikan, R. A. and Bowen, I. S. (1924) Extreme ultra-violet spectra. Physical Review, 23 (1). pp. 1-34. ISSN 0031-899X. http://resolver.caltech.edu/CaltechAUTHORS:MILpr24
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Extreme ultra-violet spectra, to 136 A, of twenty light elements, H to Cu.—Using the vacuum apparatus and explosive spark previously described, many plates have been made with a great variety of electrodes. By measuring and comparing thirty of these, over 800 lines between 136 A and 1862 A have been identified as belonging to one or other of the twenty elements studied. For H(1) only two lines, members of the Lyman series, were found; for He(2), and Li(3) none, though carefully looked for; for Be(4) one doubtful weak line; for Na(11) one strong line λ372.3 and one doubtful one λ376.6; for the other elements B(5), C(6), N(7), O(8), F(9), Mg(12), Al(13), Si(14), P(15), S(16), Cl(17), K(19), Ca(20), Cr(24) and Cu(29) from 9 to 160 lines each, all given in Tables. The strongest lines for each of the light elements are L series lines and form a progression like Moseley's for x-ray lines: Li (red), Be 3131.19, B 2066.2, C 1335.0, N 1085.2, O 834.0, F 656.4, Na 372.3, Mg 231.6, Al 162.4. These are mainly doublets, the separation increasing regularly with atomic number. M spectra also extend to shorter wave-lengths the higher the atomic number, reaching about 155 A for Cu, but on account of the complexity of the spectra only a few lines have been identified. Other series lines identified are: 2 diffuse series lines and 2 sharp series lines due to Mg+ or Mg(II), 5 lines due to Al+ and 9 due to Al++ or Al(III), 11 lines due to Si(IV) and probably the first terms of the principal series and of the diffuse series of P(V). Interpretation in terms of Bohr theory. By use of the Kossel equation in connection with available data it is shown that for Na, 372.3 A corresponds to an electron jump from the M shell to L(I); for Mg, 320.9, and 323.2 and 231.6 correspond to M(I)→L(II), M(I)→L(III) and M(III)→L(I); for Al, 162.4, 200.0, 230.8, 186.9 may correspond to jumps from shell 3 to the L shell; for Ca, 655.9 and 669.6 correspond to jumps N(I)→M(II) and N(I)→M(III). These interpretations give values of constants of the L and M levels of the atoms as follows: For Na, L(I), ν/R=2.826; for Mg, L(I) 4.298, L(II) 3.402, L(III) 3.381; for Al, L(I) 6.045, L(II) L(III) 5.008. The square roots of these values are linear functions of the atomic number. For Ca M(II), ν/R=1. 839, M(III) 1.810. From the difference L(II)—L(III) for Mg, the screening constant comes out 3.1; from the difference M(III)—M(II) for Ca, the constant is 7. These results are all in good agreement with other data. Ionization produced by explosive spark in vacuum.—The strongest spectrum lines are generally emitted by stripped atoms, that is atoms with no valence electrons left, Na(I), Mg(II), Al(III), Si(IV), P(V), etc.
|Additional Information:||©1924 The American Physical Society. Received 15 September 1923.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||25 Mar 2006|
|Last Modified:||26 Dec 2012 08:48|
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