Extreme Ultra—violet Spectra

Abstract

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 $\lambda 372.3$ and one doubtful one $\lambda 376.6$; 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 ${\mathrm{Mg}}^{+}$ or Mg(II), 5 lines due to ${\mathrm{Al}}^{+}$ and 9 due to ${\mathrm{Al}}^{++}$ 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), $\frac{\nu }{R}=2.826\mathrm{}$; 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), $\frac{\nu }{R}=1.\mathrm{}839$, 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.