ANALYTICAL CHEMISTRY
18
'
(4) Ibid., 20, 735 (1949). (5) Am. Sac. Testing Materials, B u l l . 160, 18 (September 1949). (6) Arndt, U. W., J . Sci. Instruments, 25, 414 (1948). (7) Ibid., 26, 45 (1949). (8) Arnell, J. C., and Barss, W. M., Can. J . Research, 26A, 236 (1948). (9) Baeneiger, N. C., J . Chem. Phys., 16, 1175 (1948). (10) Beatty, S., Am. Mineral., 34, 74 (1949). (11) Beatty, S., Phys. Rev., 75, 700 (1948). (12) Bergmann, M.,and Fankuchen, I., Rev. Sci. Instruments, 20, 696 (1949). (13) Bertaut, F., Compt. rend., 228, 492 (1949). (14) Blayden, H. E., Gibson, J., and Riley, H. L., J . Chem. Soc., 1948, 1693. (15) Boyd, T. F., MacQueen, J. M., and Stacey, I., ANAL.CHEM., 21,731 (1949). (16) Brindley, G. W., Xature, 164, 320 (1949). (17) Caillere, S., and Henin, S., Mineralog. Mag., 28, 606 (1949). I n d . Eng. Chem., 41, 644 (1949). (18) Carlson, H. 8., (19) Christ, C. L., Barnes, R. B., and Williams, E. F., ANAL.CHEM., 20, 789 (1948). (20) Christ, C. L., Burton, J. C., and Batty, M. C., Science, 108, 91 (1948). (21) Christ, C. L., Champaygne, E. F., Barnes, R. B., and Salzman, C. F., Jr., Reo. Sci. Instruments, 19, 872 (1948). (22) Clark, G. L., et al., "Chemistry of Penicillin," ed. by H. T. Clarke et al., pp. 267-81, Princeton, N. J., Princeton University Press, 1949. (23) Clifton, D. F., and Smith, C. S., Reo. Sci. Instruments, 20, 583 (1949). (24) Cordovi, M., Steel, 123, No. 25, 88 (1948). (25) De Wolff, P. M., Acta Cryst., 1, 207 (1948). (26) Duwez, P., and Odell, F., J . Am. Ceram. Soc., 32, 180 (1949). (27) Edwards, J. W.,Speiser, R., and Johnston, H. L., Rev. Sci. Instruments, 20, 343 (1949). (28) Esch, JV., and Schneider, A , , 2. anorg. Chem., 257,254 (1948). (29) Evans, R. C., Hirsch, P. B., and Kellar, J. N., Acta Cryst., 1, 124 (1948). (30) Fournier, F., Compt. rend., 227, 838 (1948). Phus.. (31) Geisler. A. H.. Hill. J. K.. and Newkirk. J. B., J . Applied -. 19, 1041 (1948). (32) Glemser, O., Sauer, H., and Konig, P., Z. anorg. Chem., 257, 241 (1948). (33) Grenall, A,, I n d . Eng. Chem., 40, 2148 (1948). (34) Grill, E. J., and Weber, A. H., Rev. Sci. Instruments, 20, 532 (1949). (35) Hagolston, P. J., and Dunn, H. W., Ibid., 20, 373 (1949). (36) Hattiangdi, G. S., J . Research X a t l . B u r . Standards, 42, 331 ( 1949). (37) Heal, H. T., and Savage, J., h'ature, 164, 105 (1949). (38) Hofer, J. E., Cohn, E. M., and Peebles, W. C., J . Am. Chem. Soc., 71, 189 (1949). (39) Hoffman, 0. A , , Rev. Sci. Instruments, 19, 277 (1948). (40) Jack, K. H., Proc. R o y . Soc., A195, 34 (1948). (41) Ibid., p. 41. (42) Ibid., p. 56. (43) Jellinek, hl. H., Rev. Sci. I n s t w m e n t s , 20, 368 (1949). (44) . , Jellinek. M . H.. and Fankuchen, I., I n d . Eng. Chem., 41, 2259 (1949). (45) Kaesberg, P., Ritland, H. N., and Beerman, W. W., Phys. Rev., 74, 71 (1948).
(46) Kaufman, H. S., and Fankuchen, I., ANAL.CHEM., 21, 24 (1949). (47) Kaufman, H. S., and Fankuchen, I., Rev. Sci. Instruments, 20. 733 (1949). (48) Lander, J. J., J . Electrochem. Soc., 95, No. 4, 174 (1949). (49) Lander, J. J., Reo. Sci. Instruments, 20, 82 (1949). (50) Levin, E. M., and Mchlurdie, H. F., J. Research h'atl. B u r . Standards. 42, 131 (1949). (51) Lipscomb, W. N., Acta Cryst., in press. (52) Lund, L. H., and Vineyard, G. H., J . Applied Phys., 20, 593 (1949). (53) McCreery, G. L., J . Am. Ceram. Soc., 32, 141 (1949). (54) McCrone, W. C., AXAL.CHEM.,21, 191, 306, 421, 531, 645, 767, 882, 1016, 1151, 1293, 1428, 1583 (1949). (55) MacEwan, D. M. C., Research, 2, 459 (1949). (56) Mchlurdie, H. F., and Golovato, E., J . Research ;YatZ. B u r . Standards, 41, 589 (1948). (57) Matthews, F. W., A~YAL. CHEM.,21, 1172 (1949). (58) Matthews, F. W.,and McIntosh, A. O., Reu. Sci. Instruments. 20, 365 (1949). (59) hlilligan, W. O., TT7att, M. L., and Rachford, H. H., J . Phys. & Colloid Chem., 53, 227 (1949). (60) Mysels, K. J., I n d . Eng. Chem., 41, 1435 (1949). (61) Nickels, J. E., Fineman, M .-4., and Wallace, W.E., J . Phys. & Colloid Chem., 53, 625 (1949). (62) Papp, G., and Sasvari, K., J . Applied Phys., 19, 1182 (1948). (63) Parsons, J., and Knock, S. G., Rev. Sci. Instruments, 19, 722 (1948). (64) Ritter, H. L., and Erich, L. C., ANAL.CHEM.,20, 665 (1948). (65) Rooksby, H. P., Analyst, 73,326 (1948). (66) Bustum, R. J., J . Am. Ceram. Soc., 32, 202 (1949). (67) Sage, M., Compt. rend., 228, 572 (1949). (68) Senti, F. R., and Warner, R. C., J . Am. Chem. Soc., 70, 3318 (1948). (69) Steward, E. G., J . Sci. Instruments, Phys. I n d . , 25, 331 (1948). (70) Stewart, C. B., and Lutton, E. S., J. Applied Phys., 19, 507 (1948). (71) Stolkowski, J., Compt. rend., 226, 933 (1948). (72) Straumanis, M. E., J . Applied Phys., 20, 726 (1949). (73) Stroupe, J. D., J . Am. Chem. Soc., 71, 569 (1949). (74) Switeer, G., Axelrod, J., Lindberg, M. L., and Larsen, E. S., U. S. Geol. Survey, Circ. 29 (1948). (75) Szabo, N.,and Tobias, C. W.,J . Am. Chem. Soc., 71, 1882 (1949). (76) Taylor, A., J . Sci. Instruments, 26, 226 (1949). (77) Told, R. O., and Hattiangdi, G. S., I d . Eng. Chem., 41, 2311 (1949). (78) Walker, G. F., A'ature, 164,577 (1949). (79) Warekois, E. P., Rev. Sci. Instruments, 19, 607 (1948). (80) Warren, B. C., J . Applied Phys., 20, 96 (1949). (81) Watt, G. W.,and Davies, D. D., J. Am. Chem. Soc., 70, 3751 (1948). (82) Wooley, R. L., J. Sci. Instruments, 25, 321 (1948). (83) Wooster, W.A., Ramachandran, G. N., and Lang, A., Ibid., 26, 156 (1949). (84) Wright, B. A , , and Cole, P., Rev. Sci. Instruments, 20, 355 (1949). (85) Yudowitch, K. L., J . Applied Phys., 20, 174 (1949). (86) Zachariasen, W. H., Acta Cryst., 1, 285 (1948). (87) Zachariasen, W.H., Am. Mineral., 33,783 (1948). RECEIVED December 19, 1949.
EMISSION SPECTROSCOPY WILLIAM F. MEGGERS, National Bureau of Standards, Washington, D. C.
L
AST year the writer (69) reviewed the principal spectro-
scopic advances in fundamental research and applications for three postwar years including most of 1948; that review is hereby extended to 1949. Because the quantum interpretation of atomic spectra contributed so greatly to knowledge of atomic structure and other properties of atoms, basic research in spectroscopy was intensive, and world Fide until 1940. Then emphasis in physical research shifted suddenly t o ballistics, aerodynamics, electronics, and atomic energy for military purposes. Ten years later this emphasis is unchanged but, thanks mainly to a few faithful prewar spectroscopists, progress has been made in standard wave
lengths, term analysis, Zeeman effect, isotope shifts, hyperfine structure, and new elements. STANDARD WAVE LENGTHS
The chain-reacting uranium piles, primarily constructed for making atomic bombs, have yielded artificial elements that are of inestimable value to science-for example, the abundance of neutrons from :XU fission makes possible plentiful production of pure '18Hg by transmuting " ~ A u . Spectroscopic light sources containing this artificial isotope of mercury emit spectral lines of greater sharpness than any found in nature and the wave length
V O L U M E 2 2 , NO. 1, J A N U A R Y 1 9 5 0 of the green line of Ig880Hg has been proposed ( 7 0 ) as the ultimate etandard of length. Preliminary measurements of the wave have been relengths of the green and yellow lines of ’::Hg ported ( 8 2 )by the Kational Bureau of Standards in Washington. the Kational Physical Laboratory near London, and the International Bureau 2f Teights and Measures near Paris. The values in International Angstroms are: X.B.S.
N.P.L.
5460.7532 5769.5983 5790.6628
5460.7531 5769.5985 5790.6628
I.B.W.M. 5460.7533 5769.5986 5790.6630
Mean 5460.7532 5769.5985 5790.6629
This is probably the first time in history when three different nations have come so close to nearly perfect agreement. The only other contribution in recent years to precise measurements of wave lengths by interferometer technique is by Burns and Sullivan ( 1 7 ) , who observed the spectrum of nickel in the vacuum arc from 2173 to 8968 They ako reported some wave lengths of cobalt, titanium, manganese, magnesium, chromium, and aluminum lines observed incidentally as impurities in nickel. TERiM ANALYSIS
Although hydrogen emits the simplest of all spectra, it has been the subject of more than 1000 spectroscopic papers. The spectrum of hydrogen has a h e structure which, according to the Dirac wave equation for an electron moving in a Coulomb field, is due to the combined effects of relativistic variation of mass with and velocity and spin-orbit coupling. The ground state is 1s zS~/2 and 22, 2P‘11 ), 3 ) 2 . According to the first excited states are 2s the Dirac theory the 2s 2S1,2state coincides exactly with 2p 2 P o ~ / 2 . Experimental attempts to confirm this through a study of the Balmer lines have been frustrated by the large Doppler width of the lines in comparison with the splitting of the n = 2 states, which is about 0.36 cm.-’ for 2 2P1/2 - 2 zP3/2. However, the great wartime advances in microwave techniques provided new methods for a study of the n = 2 states of the hydrogen atom. Such a study by Lamb and Retherford (60) indicated clearly that the 2 2Sl/sstate is higher than the 2 zP1,2state by about 1062 megacycles per second, or 0.035 cm. This result inspired several conventional~spectroscopists to look for an analogous shift of S-levels in the hydrogenlike spectrum of ionized helium, and such investigations have been reported by and Hirschberg and Fowles ( 2 9 ) , Kopfermann and Paul (64), Mack ( 4 1 ) . Microwave techniques were applied to this problem by Skinner aud Lamb ( 9 4 ) . Sotable extensions of the principal series have been observed in the absorption spectra of sodium, potassium, rubidium, and cesium. Thus, McXally ( 6 3 ) measured the sodium series to 3% - 522P0,while Thackeray ( 9 8 )observed it to 7gZP0. Kratz (66) reported observations on the principal series of potassium to 7g2Po,rubidium to 772P”,and cesium to 732P0. lIc?jally et al. (66) observed the cesium series to the G2nd member. These Icng, regular series have been extrapolated to limits from which five- or six-figure ionization potentials can be derived. In addition to these principal series, Kratz and Alack ( 6 7 )have observed in longpath absorption “forbidden” lines of type 2% - nzD to 132Dfor potassium, 212Dfor cesium. Apath of 24 meters of rubidiumvapor at 278” C. slhowed 5% - nl lines to 5PD and also from 2g2F”t o 5O2F0and from 29 q to 47 q where q is the 1 value of nonpenetrating electrons with 1 > 3. With much difficulty Vancouleurs (102) extended obscrvation of potassium subordinate series in emission from 42P0 - 112D to 162Dand 42P0- 13% to 1PS. By observing the hollow-cathode spectrum of cadmium over the wave-length range 600 to 6600 A., Shenstone and Pittinger (90) were able to refine and extend data and analysis for the first three spectra of cadmium and calculate 37.6 electron volts as the third ionization potential. Recent improvements in infrared spectrometers and detectors have been applied to observations of the spectra of noble gases
19 beyond the long-wave limit accessible to photography. Marly ~ observed for argon, krypton, new lines between 1.2 and 2 . 2 were and xenon by Sittner and Peck ( 9 3 ) ,and by Humphreys (44) who also observed neon and classified practically all new lines as combinations of known and new levels, particularly those arising from the s2pEf1configuration. Sotable progress in the description and analysis of complex atomic spectra can be reported for chromium, manganese, tantalum, technetium, uranium, neon, argon, krypton, and xenon, although the details are mostly still unpublished. Kiess ( 4 9 ) remeasured arc, spark, and Zeeman spectrograms of chromium and has practically completed the structural analysis of Cr I and Cr II spectra by finding atomic energy levels that account for ca. 2800 Cr I and 1400 Cr 11 lines. The Cr 111spectrum was investigated by LIoore ( 7 6 ) ,who found 41 terms that accounted for 583 lines; he is also investigating the spectrum of trebly ionized chromium. Completely new measurements of arc, spark, and Zeeman spectra of manganese permitted Catalin (19) finally to complete the analysis of Mn I which he began in 1921. Catalin’s discovery in chromium and manganese spectra of terms with five or six levels each was the catalyst for the interpretation of complex spectra and development of quantum theory. Catalan first proposed that a group of lines resulting from the combination of tn-o complex terms be called “a multiplet”; he has now recognized more than -100 such multiplets in the l l n I spectrum comprising about 2000 lines. Catalin is also working on the M n 111 spectrum, while Curtis ( 2 2 ) is extending t,he analysis of Mn 11 that he published a dozen years ago. The kmve lengths and relative intensities of more than 2000 lines characteristic of the first tn-o spectra of technetium (a uranium-fission product) have been drtermined by Meggers and Scribner ( 7 1 ) , who have also classified the stronger lines of Tc I and Tc 11 spectra as combinations of identified sextet and septet terms, respectively. The ground state of 43Tc atoms is established as (4djSs2)6821/, but the lowD only 2572.9 cm.-l higher. est energy level of ( 4 d 5 ~ ’ ) ~is The wave lengths of several thousand lines characteristic of promethium (another uranium-fission product) have been measured by Meggers and Scribner ( 7 2 ) but the data are still inadequate for the differentiation of successive spectra or the analysi~ of spectral structure. They confirm, however, the discovery of a new element of rare-earth type-viz., 8,Pm. The arc and spark spectra of &e have been photographed with pure metal electrodes to provide complete and accurate data for the final anslysis of Re I and Re 11 spectra. The observed wave lengths range from 2000 to 12,000 -1. Investigation of the spectra of tantalum has been in progress for many years; a preliminary report on t e r m and magnetic splitting factors established for T a 11 was recently sent to press by-Kiess et al. (50). Progress in the analysis of the second spectrum of WE,supported by Zeeman effect, has been reported from the AIassachusett,s Institute of Technology (65) and from the Zeeman Laboratory ( 7 ) . In the latter a search for connections between two independent groups of classified lines failed but added 17 levels to one group and 63 to the other, thereby increasing the number of classified lines by 392 to a t,otal of 743. The relative energy of levels from 5f47s1 and 5f37sz is still unknown. The spectra of the heavy elements, protactinium, neptunium. plutonium, and americium, like those of thorium and uranium. are characterized by very great complexity. Consequently, descriptions of these spectra to be adequate for term analysis and assignment of electron configurations must include accurately measured wave lengths, relative intensities, excitation criteria for thousands of lines, and resolved Zeeman patterns for the stronger ones. Because considerable effort and amounts of sample are required, it will be some time before such descriptions are available. I t may be presumed that the production and purification of these ponderous particles ail1 be controlled by spectrochemical analysis. For this purpose it is sufficient to have approximate wave lengths and calibrated intensities of prominent lines in a
ANALYTICAL CHEMISTRY
20 convenient spectral region. Tomkins and Fred (100) have published such data for 263 lines of protactinium from 2640.3 to 4371.78., 114linesof neptuniumfrom2655.0 to 4363.88., 220 lines of plutonium from 2677.0 to 4358.1 A., and 227 lines of americium from 2661.6 to 4374.9 A. Their line intensities are proportional to the reciprocal of the limiting dilutions a t which they could be recorded photographically with a copper spark source and a 3-meter grating spectrograph. A striking resemblance of americium and europium spectra (both elements have a few lines of outstanding intensity) suggests by analogy that americium has in its normal state seven 5f electrons and two 7s electrons. Relatively little has been done recently on atomic spectra beyond the IIIrd. (EdlBn is building a new physical laboratory in Sweden, and in the United States all prewar vacuum spectrographs are still idle except one a t Princeton University.) In India three spectra of multiple ionized iodine have been investigated: I 111 (bo),I VI (68), and I VII ( d 7 ) . Most of the results for spectral terms of light elements reviewed above will be found in Volume I of "Atomic Energy Levels" (74), which contains data on ionization potentials, electron configurations, spectral terms, quantum numbers, and magnetic splitting factors (where known) for 206 spectra characteristic of the first 23 atomic numbers, 1H to rsV, inclusive. The remainder (and more) will appear in future volumes of this work, Volume I1 of which (now in press or preparation) will contain similar data on all known spectra of a t least 18 atomic numbers, 2,Cr to rlKb, inclusive.
radioactive elements will be investigated in nlagneiic fields because improvements in enclosed light sources permit observations with minute samples that may be recovered for other purposes. FORBIDDEN LINES
Atomic spectra almost universally obey simple selection rules governing transitions between atomic energy levels, but from time to time "forbidden lines" are detected in various sources. Thus, three forbidden 0 I lines (5577, 6300, and 6363 A.) long ago detected in the spectrum of the aurora borealis have recently been identified by Bowen (0) and by Cabannes and Dufay (18)as faint absorption lines in the solar spectrum. Six diffuse lines (2819 to 3005 A,) attributed to Cd F are now explained (81)as Cd I forbidden transitions forced by ionic electric fields in a high-current arc. This example shows that it is easy to mistake asymmetrical atomic lines for band heads as well as vice versa. A suggestion that forbidden lines in the spectra of saZn, &d, and saHg arise from the magnetic moments of isotopic nuclei with odd-mass numbers was tested for 4&d by Deloume and Holmes (23),who compared the intensities of 3320 A. (53Pi - 51S0) and 3141 A. (53Pi - 5%) emitted by an electrodeless discharge in natural cadmium vapor containing 23% ':iCd, with the same lines emitted by cadmium vapor enriched with 64.5% 'iiCd, and reported that the intensities of the forbidden lines were indeed proportional to the abundance of '2:Cd.
ZEEMAN EFFECT
ISOTOPE SHIFTS
Because the Zeeman effect is the most effective aid in the analysis and interpretation of spectra, further observations of line splitting and polarization in magnetic fields are urgently needed. Such observations have been reported recently for Au I and Au 11by Green and Maxwell (34) and for U I and U 11 by Bosch and Berg (8). In uranium magnetic splitting factors (g-values) are given for 37 U I levels and for 82 U 11 levels. In both gold and uranium departures from LS-coupling of the optical electrons are indicated by the observed magnetic splitting of spectral lines. The paper by Kiess and Shortley (51)on the Zeeman effect for nitrogen and oxygen is important not only because these are the lightest elements for which magnetic splitting factors have been determined, but also because it shows for the first time hon g-values are properly derived from unsymmetrical Zeeman patterns exhibiting partial Paschen-Back effect, which is all too common in many spectra. The diamagnetic quadratic Zeeman effect in the principal series of K I, Rb I, and Cs I spectra has been investigated by Harting and Klinkenberg (97). This effect originates in atomic diamagnetism and is therefore proportional to the mean square of the radius of the electron orbit, or to the fourth power of the effective quantum number. I t results in a quadratic shift of high levels, giving rise to a quadratic displacement of the magnetic components to shorter wave lengths. Measurements were made on wave lengths of absorption lines to effective quantum numbers exceeding 30, in magnetic fields of 22,600 oersteds, and the observed displacements were found to agree closely with those predicted. Zeeman spectrograms made in the Spectroscopy Laboratory a t the Massachusetts Institute of Technology have recently been measured for the derivation of g-values of the Mn I and Mn 11 terms (19) and of Fe 11 terms (104). After 10 years of regretted interruption, the M.I.T. Zeeman-effect program was resumed in 1949 when superior Zeeman spectrograms were obtained with arcs of &r, ZbMn, MRU,7zHf, rrTa, 75Re,76oP, and 7711. in magnetic fields of 80,000 to 90,000 oersteds. This practically completes the observation of Zeeman effect for most of the common metals, but a great deal still remains to be done with rare earths, whereas the investigation of Zeeman effect for unstable elements created either by transmutation or by hsion has only been suggested. There are good prospects that radiations from extremely rare and
The spectra of hydrogen, deuterium, and tritium differ slightly and progressively, primarily because the isotopic nuclei have different masses. Indeed, this fact was the inspiration for the discovery of heavy hydrogen. Later studies in other spectra made it appear that factors other than mass contributed to the observed displacements, but up to the present time no satisfactory theory of isotopic shifts has been developed. Last year Andrew and Carter ( 2 ) reported measurements of the isotope shift of the red line (6678 A.) of :He relative to :He in agreement with the theory of Hughes and Eckart. Other measurements on the same and on other rHe lirias by Bradley and Kuhn (IO),by Manning (68), and by Fred et al. ( S I ) are neither in close agreement with each other nor IFith the theory. Preliminary results on the line shifts of ::Se relative to TiSe have been reported by Murakawa and Suwa (78)for nine lines (3319.8 to 3727.1 A.) of the Ne 11spectrum. I t appears that lines of the doublet system show larger isotope shifts than those of the quartet system. Because the isotope shift of Ba I lines is too small to observe by usual methods, Kopfermann and Wessel (5b) studied the resonance line 5536 A. in absorption of an atomic beam illuminated by light from a hollow cathode, and concluded that two barium isotopes differing by two units of mass shou line shifts of 0.012 * 0.002 cni. -l Isotope shifts in the spectrum of &m have been carefullyheasured by Brix and Kopfermann (11, I S ) and by Briv ( I d ) . Comparison (11) with earlier results for BoNd leads to the discovery that isotopes with equal numbers of neutrons (but different numbers of protons) show the same isotope shifts of spectral lines. Brix ( I d ) measured b",'Sm - '&Sm isotope shifts of 80 lines of Sm I between 5044 and 7132 A. The lines were sorted into several groups according to magnitude and sign of shift, which in turn were correlated with atomic energy levels. This analysis of isotope shifts confirmed almost completely the term analysis of Albertson, and added four nen- levels. Furthermore, it was possible with isotope shifts to group many of the observed levels into terms and assign the proper electron configuration. This is the first instance in which isotope shifts have made a real contribution to the structural analysis of a complex spectrum. Isotope shifts among hundreds of lines (2500 to 4800 A.) ';$,, and ' ~ ~were U obemitted by uranium isotopes 2 ~ ~ U
21
V O L U M E 2 2 , NO. 1, J A N U A R Y 1 9 5 0 served by Burkhart et al. (16), who concluded that any line shifted from ‘;:U to ‘i5U was also shifted from ‘;gU to ‘@,U, that the direction of shift of lighter isotopes is generally toward shorter waves, and that there appeared to be no correlation between the actual shifts and the mass numbers. When McNally ( 6 4 ) compared the isotope shifts in uranium spectra with U I and U 11 energy levels and electron configurations, he found a simple shift arising from an interaction of a configuration with a nucleus, a complex shift arising from perturbations between close-lying levels, and the largest shifts involved configurations containing sz electrons, indicating an additive type of interaction for the s-electrons and the nuclei. So long as there is no adequate theory or general understanding of isotope shifts, it is perfectly proper to grope for correlations and generalizations. How else can one hope to stumble upon the basic laws of nuclear physics? HYPERFINE STRUCTURE
When optical electrons interact with atomic nuclei that possess magnetic momenta, the spectral lines are split into hyperfine components which, if resolved and measured, lead to quantitative determination of the mechanical, magnetic, and quadrupole moments of the nuclei. There is no ambiguity about the theory and interpretation of hyperfine structure; the only difficulty is an understanding of the manner in which the observed properties of nuclei can be compounded from the known properties of the elementary particles that comprise the nuclei. I n the meantime rapid progress is being made in the accumulation of data on properties of nuclei. From grating spectrograms of P 111and P IV lines exhibiting hyperfine structure Crawford and Levinson (21) have deduced for :AP a spin of 1/2(h/2~)and a magnetic moment of 1.15 nuclear magnetons. The hyperfine structure of AI 11 lines (6226, 6231, and 6243 A , ) was resolved with interferometers by Suwa (97) who found gocd agreement with theory even when the fine structure separations are small. The hfs of an 80% enriched isotope ‘EiTe was found by Foales (30)to consist of doublets with intensity ratio 3 to 1, indicating a spin of I/*. Enriched samples of $e and ’ 2 T e in the hands of Mack and Arroe (62) indicated for the former a spin greater than l / 2 , and for the latter The electron structure of slTe is not sufficiently well known to determine the nuclear magnetic moment, but the hfs splitting of the two isotopes is found to be identical except for a scale factor which yields the tentative value plLj/p1?7 = 1.208 for the ratio of the moments. For an enriched sample of PZZr, Arroe and Alack ( 4 )found a spin of 5 / 2 . S o hyperfine structuie could be detected in enriched samples of $iFe either by Gurevitch and Teasdale (35) or by Brossel (15). It is pointed out ( 3 5 ) that many elements with odd atomic mass but even nuclear charge have no measurable magnetic moment. The hyperfine structure of electromagiietically separated isotopes of f i X e and jiI
