UtanTiaST-** Reference book not to be j4jLiit» taken irom the Library nbs circular 518 Molecular Microwave Spectra Tables UNITED STATES DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS Related Publications Atomic Energy Levels A critically evaluated compilation of all known data on the energy levels of elements, designed to meet th< needs of workers in nuclear and atomic physics, astrophysics, chemistry, and industry. Energy levels o: elements of atomic No. 1 through No. 41 appear in the first two volumes. Future volumes will contair those of the other elements. Spectra are presented in order of increasing atomic number, and under a given atomic number they are listec in order of increasing stages of ionization. For each spectrum there is a selected bibliography covering the analysis. The energy levels are tabulated in the related groups that form spectroscopic terms, counting upward from the lowest as zero. Also given in the tables are electron configurations, term intervals, Land* g-values, and term designations in a uniform notation. For the more complex spectra, arrays of observed terms and their electron configurations are included. The introduction contains similar arrays of the terms predicted by theory for important isoelectronic sequences. National Bureau of Standards Circular 467: Volume I, $2.75. Nuclear Data A comprehensive collection of experimental values of half-lives, radiation energies, relative isotopic abun¬ dances, nuclear moments, and cross sections. Decay schemes and level diagrams are provided wherever possible. The tables are a valuable tool for nuclear physicists and engineers, radiochemists, biophysicists, and other workers in nuclear physics. At present over 1,000 new measurements of different nuclear properties are being reported each year in some thirty different journals and in the reports of dozens of different laboratories. Supplements appearing at 6-month intervals will keep these tables current. References to literature in the field, a list of journals surveyed in compiling the tables, and a current list of fission and spallation papers are included. National Bureau of Standards Circular 499 arid the first three supplements, $4.25. Electric Quadrupole Coupling of the Nuclear Spin with the Rotation of a Polar Diatomic Molecule in an External Electric Field This paper first reviews the qualitative aspects of molecular rotation in an electric field, disregarding the effects that give rise to a hyperfine spectrum. It then gives formulas that serve to determine the hyperfine spectrum of a rotating molecule in various cases, depending on the external field strength and on the rotational quantum number. Also included are applications of the general expression for the quadrupole interaction matrix to several special cases. National Bureau of Standards Research Paper RP1866, 15 cents. Order all publications from the Superintendent of Documents, United States Government Printing Office, Washington 25, D. C., at listed prices. Foreign remittances must be in United States exchange and should include one-third the publication price to cover mailing costs. UNITED STATES DEPARTMENT OF COMMERCE • Charles Sawyer, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astm, Acting Director Molecular Microwave Spectra Tables Paul Kisliuk and Charles H. Townes National Bureau of Standards Circular 518 Issued June 23, 1952 For sale by the Superintendent of Documents, U. S. Goverrnment Printing Office Washington 25, D. C. - Price 65 cents Contents Page 1. Introduction_ i 2. Description of tables_ m Symbols_ vi References___ vi 3. Molecular microwave spectra tables: I. Molecules listed alphabetically by chemical symbol_ 1 II. Lines listed in order of frequency_ 91 III. Casimir’s Function for J=1 —> 10, 1=1 —» 9/2, values of [3/4C(C +1)—1(1 + 1) J(J -f l)]/2l(2l —1)(2J— 1)(2J + 3), where C=F(F+1) —1(1 + 1)—J(J+1)_ 115 4. Indexes: I. Molecules by chemical symbol_ 120 II. Molecules by name_ 122 III. Authors listed alphabetically, including a list of the molecules with the reference numbers_ 124 Acknowledgment The authors are grateful for the encouragement and interest of H. Lyons and R. G. Nuckolls, and for the latter’s considerable aid in editing the tables. J. R. Madigan and L. J. Rueger of the National Bureau of Standards, and L. C. Aamodt and G. Dousmanis of Columbia University have also helped substantially in calculating, compiling, and checking the information in these tables. Molecular Microwave Spectra Tables Paul Kisliuk and Charles H. Townes1 This group of tables gives the frequencies, assignment of quantum numbers, and intensities of about 1,800 microwave absorption lines. The best available values of other pertinent molecular data, such as rotational constants, dipole moments, quadrupole coupling constants, and rotation-vibration interaction constants are also included. The frequencies are listed once for each molecule, and again in consecutive ascending order of frequency. References are given for all data included. For easy calculation of quadrupole hypernne structure, Casimir’s function is tabulated up to J = 10, and 1 = 9/2. Explanations of the tables and a short discussion of microwave spectra and important formulas are given in the introduction. 1. Introduction These tables of microwave spectra are a modern¬ atomic hydrogen and cesium that fall in the micro- ization and revision of those published in the wave region. Microwave absorption in para¬ Journal of Research of the National Bureau of magnetic gases due to transitions between Zeeman Standards [l].2 They are up to date as of Novem¬ components has also been observed, but is not ber 15, 1950, so far as published material is con¬ included here. cerned, and include a considerable amount of The considerable activity in microwave spec¬ otherwise unpublished information. However, troscopy makes obsolescence of the present tables since many of the published results have been inevitable, arid it is expected that they will be reported rather briefly, it is clear that for certain revised and republished from time to time. Sug¬ molecules more detailed information is available gestions or additions for future editions of these in the experimental laboratories than is included tables will be gladly received, by either the authors or the Microwave Standards Section, National here. Only molecular lines of frequency greater than Bureau of Standards, Washington, D. C. It is 1,000 megacycles have been listed. This excludes especially hoped that information obtained on nuclear resonances found by molecular beam microwave spectral lines that is not otherwise techniques rather than the usual microwave published will be received so that it may be absorption measurements, as well as the lines of included in the tables, and thus made available. 2. Description of Tables The primary information is presented in an seemed no reason for preference. Frequencies alphabetic listing of the molecules, which is sub¬ listed to the nearest megacycle were generally divided according to the major quantum numbers measured with a cavity wavemeter and are subject involved in the transition. Hyperfine components to an error of 10 or more megacycles, whereas and unidentified transitions are presented in order those given to a fraction of a megacycle are gener¬ of frequency. With the listing of each molecule, ally known to an accuracy of about 0.1 megacycle. all available molecular constants are given that In addition to the absorption lines actually are needed in interpreting the spectra. These observed and listed, a large number of lines may include rotational constants, dipole moments, be readily and accurately predicted with the help quadrupole coupling constants, and rotation- of molecular constants given in the tables. vibration interaction constants. In addition to Another listing of all the lines in order of fre¬ quency, with sufficient information to locate the the observed frequency and the transition assigned lines in table I, is included together with a classi¬ to each line, there is included a calculated value for fication of the lines as strong, medium, or weak. the intensity, and references to the latest sources The authors have arbitrarily taken lines of maxi¬ of data from each laboratory that has measured mum absorption coefficient less than 5X10 Tun the line. The most precise reported values of the as weak, those from 5X10-7 to 10-5cm 1 as medium frequencies were used, or the average, if there and those greater than 10-5cm_l as strong. The general characteristics of the microwave 1 Consultant, National Bureau of Standards, Washington 25, D. C. spectra of most molecules may be explained on 2 Figures in brackets indicate the literature references given on page vi. the basis of a nearly rigid rotator model. Mole¬ cules are conveniently divided into three classes: linear molecules, symmetric tops, and asymmetric tops. For linear molecules the frequency of pure 3/4 C(C+!)-/(/+1)J(J+1)1 rotational lines is given to a good approximation 2(2J+3)(2«7-1)7(27-1) J’ by [2]: where vj_^j+1 = 2(J-\-\)Bv—^I)j{ («7-f l)3—(«7+l)Z2} sec"1 C=F(F+1)-/(/+!)-J(J+1) F=J+I, J+I-1 .... \J-I\ while for symmetric top molecules, where the selection rule AK = 0 applies; eqQ=quadrupole coupling constant as defined in reference [7] vj->j+i = 2(e7 + l)Bv—4Dj(J +1)3 K= projection of J on molecular symmetry axis — 2Djk(J+ 1)K2 sec-1. (zero for linear molecules in the ground vibrational state). In both cases: A tabulation of the function in square brackets for J= 1 to 10 is given in table III. The some¬ p_A/l\ ~ what more complex situation when two nuclei have ' 8tT2 \7»/„ = quadrupole coupling is discussed in [7]. N uclear quadrupole effects in a symmetric mol¬ where ecule may be described by a single coupling con¬ stant (eqQ), where e is the protonic charge, Q the *7= the total rotational momentum quantum nuclear quadrupole moment, and q=d2V/da2 is number the second derivative along the molecular axis of l, 7C=the rotational momenta quantum num¬ the potential at the nucleus due to all charges out¬ bers along the figure axis for linear side the nucleus.