JANUARY, 1949JOURNAL OF THE OPTICAL SOCIETY OF AMERICA

High Members of the Principal Series in Caesium

J. RAND McNALLY, JR.,* JULIUS P. MOLNAR,** WILLIAM J. HITCHCOCK,*** AND NORMAN F. OLIvERt

Massachusetts Institute of Technology, Cambridge, Massachusetts

(Received August 30, 1948)

The results of an investigation initiated several years ago are presented in summary form.

The more intense doublet member of the principal series of caesium in absorption is recorded

to the sixty-second quantum state, whereas the weaker doublet member is recorded to the

fourteenth quantum state only. An empirical formula fitting the longer series to about 0.03

cm-' is given. The calculated series limit of 31406.32 cm-' corresponds to an ionization potentialof 3.8929 volts for the caesium atom.

PHOTOGRAPHS of the principal series ofcaesium in absorption, taken in the MIT

Spectroscopy Laboratory prior to World War II,have been found to show higher series members

than previously reported. Bacher and Goudsmit 1

list the n 1 1° series to the n=36th quantumstate. Kratz and Mack2 have reported observingresolved doublets to n = 15p and the 1V seriesof levels to 66, although no detailed data havebeen published by them. In this note we list

the higher series doublet members from n=11to n = 14 and the more intense member to the62nd quantum state. The intensity ratio of thedoublet lines for the higher series members is not

in agreement with the simple theory whichpredicts a ratio of 2:1 (seeFig. 1). This difficulty

of observing complete doublets involving highquantum states in absorption has been discussedby Fermi.3

The absorption tube used in this experimentconsisted of an iron pipe approximately twoinches in diameter and about one meter longwith quartz windows Glyptalled on the ends.The tube was wrapped with asbestos and heaterwire and the current adjusted to give fairlystrong absorption of lines in the visible, thebreadths of which were used as an indication ofthe vapor density. An entirely satisfactory con-tinuum was obtained from a water-cooled,General Electric, type H-6 mercury lamp.

The absorption system was evacuated andcaesium metal, produced by heating an intimate

FIG. 1. Reproduction of sections of wave-length film illustrating intensity anomaly in the eighth member of the caesiumprincipal series doublets (at 3313A). Compare with the neighboring 3302A sodium principal series doublet.

* Now with Stable Isotopes Group, Carbide and Carbon Chemicals Corporation, Oak Ridge, Tennessee.** Now with Bell Telephone Laboratories, Murray Hill, New Jersey.*** Now with Baird Associates, Cambridge, Massachusetts.t Now at 48 Almy Street, Fall River, Massachusetts.1 R. T. Bacher and S. Goudsmit, Atomic Energy States (McGraw-Hill Book Company, Inc., New York, 1932).2 H. R. Kratz and J. E. Mack, Rev. Mod. Phys. 14, 104 (1942).3 E. Fermi, Zeits. f. Physik 59, 680 (1929.).

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VOLUME 39, NUMBER

McNALLY, JR., MOLNAR, HITCHCOCK, AND OLIVER

mixture of caesium chloride and calcium metal,was distilled into the main absorption tubewhich had been previously baked out. Thepressure of foreign gases was maintained suffici-ently low to eliminate line shifts attributable to

TABLE I. High members of the principal series in cesium,62S -g2Plio

TABLE II. High members of the principal series in caesium:6'Sj - nP1

it X

11 3400.00412 3348.73413 3314.08214 3289.318

Ut X

11 3397.99812 3347.53313 3313.15614 3288.63415 3270.50416 3256.70817 3245.94918 3237.41119 3230.50820 3224.84721 3220.15022 3216.20523 3212.85924 3210.00025 3207.53626 3205.3727 3203.52928 3201.88529 3200.42430 3199.14831 3197.99532 -33 3196.03834 3195.20635 3194.45236 3193.76137 3193.13538 3192.55939 3192.03440 3191.54841 3191.10942 3190.69943 3190.32344 3189.96945 3189.64846 3189.34847 3189.06748 3188.78749 3188.54350 3188.32151 3188.11052 3187.90853 3187.70554 3187.5555 3187.3556 3187.1657 3187.0358 3186.9159 3186.7760 3186.6561 3186.5262 3186.41

aK

29420.6929864.1930174.0530399.0330567.5530697.0330798.7830880.0030945.9831000.2931045.5231083.6031115.9631143.6831167.6031188.631206.5931222.6131236.8631249.3231260.59

31279.7331287.8731295.2731302.0331308.1631313.8131318.9631323.7331328.0431332.0531335.7631339.2331342.3931345.3431348.1031350.8531353.2531355.4331357.5131359.5031361.4931363.031365.031366.831368.131369.331370.731371.831373.231374.2

a29420.7029864.2030174.0330399.0230567.5430697.0530798.7130879.9830945.9731000.2831045.5131083.5931115.9431143.6631167.6031188.4031206.6031222.6131236.7731249.3531260.5831270.6531279.7131287.8931295.3131302.0531308.1931313.8131318.9631323.6831328.0431332.0131335.7831339.2231342.4231345.4031348.1731350.7631353.1831355.4431357.5631359.5531361.4331363.1931364.8531366.4231367.9031369.2931370.6231371.8731373.0631374.19

Aa

-0.01-0.01

0.020.010.01

-0.020.070.020.010.010.010.010.020.020.000.2

-0.010.000.09

-0.030.01

0.02-0.02-0.04-0.02-0.03

0.000.000.050.000.04

-0.020.01

-0.03-0.06-0.07

0.090.07

-0.01-0.05-0.05

0.06-0.2

0.10.40.20.00.1

-0.10.10.0

foreign gases.4 A large number of sharp lines inthe arc spectrum of iron were used as comparisonstandards, the spectra being measured on theHarrison automatic comparator.5

The higher members of the 62S - n2P1 °o seriesare given in Table I, which lists the total quan-tum number, n; the observed wave-length inair in angstroms, ; the vacuum wave numberin cm-' from Kayser,6 aK; the wave numberas calculated from the equation below, a; andthe wave number difference, GA-. Table IIgives similar information, in part, for the lessintense member of the doublet. Additional ab-sorption lines observed were: K-3446.717A;Na-3302.990A; and Na-3302.383A, the latterdisagreeing with the MIT Wavelength Tables7

average value by 0.049A.The series from n = 11 to n = 62 satisfies, to a

good approximation, the formula

a = 31406.32109,737.30

where - is the calculated wave number, n is thetotal quantum number, ,u = 3.55900, and b = 0.381.The series limit of 31406.32 cm-' corresponds toan ionization potential of 3.8929 volts. Thisseries limit differs from the value of 31404.6 cm-'obtained by Bevan.5

4 H. Margeneau and W. W. Watson, Rev. Mod. Phys.8, 22 (1936); N. Tsi-Z6 and C. Shang-Yi, J. Opt. Soc. Am.51, 568 (1937).

5 G. R. Harrison, J. Opt. Soc. Am. 25, 169 (1935);Rev. Sci. Inst. 9, 15 (1938); G. R. Harrison and J. P.Molnar, J. Opt. Soc. Am. 30, 343 (1940).

6 H. Kayser, Tabelle der Schwingungszahlen (S. Hirzel,Leipzig, 1925).

7 G. R. Harrison, MIT Wavelength Tables (John Wileyand Sons, Inc., New York, 1939).

8 p. V. Bevan, Proc. Roy. Soc. A86, 320 (1912).

58

f n -/,,+ (bl(n -g)') 1 2