Breivogel, F.W.

Hebert, A.J.

Street, K.

Hollowell, C.D.

Street, J.

eScholarship - University of California

THE RADIO-FREQUENCY AND MICROWAVE SPECTRA OF NaF BY THE MOLECULAR-BEAM ELECTRIC-RESONANCE METHOD

Lawrence Berkeley National LaboratoryRecent WorkTitleTHE RADIO-FREQUENCY AND MICROWAVE SPECTRA OF Li6I127 BY THE MOLECULAR BEAM ELECTRIC RESONANCE METHODPermalinkhttps://escholarship.org/uc/item/3hk433vcAuthorsBreivogel, F.W.Hebert, A.J.Street, K.Publication Date1964-09-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaUCRL- i 1.404 University of California Ernest O. Radiation Lawrence Laboratory TWO-WEEK lOAN COPY. This is a library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Diuision. Ext. 5545 THE RADIO-FREQUENCY AND MICROWAVE SPECTRA OF Li61127 BY THE MOLECULAR BEAM ELECTRIC RESONANCE METHOD Berkeley, California DISCLAIMER· This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof,or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily st~te or reflect those of the United States Government or any agency thereof or the Regents of the University of California. , .. ,·1 \ i Submitted to J. Chern. Phys. for publication UNIVERSITY OF CAl:.JIFQRNIA .1 La~rence Radiation Laboratory Berkeley, California AEC Contract No. W-7405-eng-48', , " < THE RADIO-FREQUENCY AND MICROWAVE SPECTRA OF Li6I l27 BY THE MOLECULAR BEAM ELECTRIC RESONANCE METHOD , . ___ .l UCRL-11404 F. W. Breivogel, Jr., A. J. Hebert, and K. Street, Jr., September 1964 " .'\ / i , ' ; '. ;; i ' I -iii- UCRL-11404 THE RADIO-FREQUENCY AND MICROWAVE SPECTRA OFLi 6Il~n ,. . * BY THE MOLECULAR BEAM ELECTRIC RESONANCE METHOD F. W. Breivogel, Jr., A. J. Hebert, and K. Street, Jr. Department of Chemistry and Lawrence Radiation Laboratory University of California . Berkeley, California September 1964 ABSTRACT . . . 6 127 . : The radio-frequency and microwave spectra of Li I have been observed by the. 'molecular-beam electric-resonanc~ method of molecular spectroscopy. Spec-tra of Li6I 127 in the first two vibrational states were obtained: From the J=l radio-frequency Stark spectra values were obtained for the electric dipole mom-ent ~, the iodine nuclear quadrupole interaction eq~; and the iodine spin-rota.t:ilon constant cI• The values of these constants are: '-v=O v=l ~ (D) 7.4285± 0.001 7~5l20 ± 0.001 eq~ (Mc/se'c) -198.780 ,+ '0'005 : ... -', :. '. . -207 .~)3 ± 0.010 cI (kc/sec) 7.7 ± 0.4 7.8 ± 0.6 The observation. of J=l ~ J=O microwave transitions yielde~ the following ~otational constants: BO = 15,304.895 ± 0~005 Me/sec Bl = 15,153.316 ±0.009 Me/sec. . > r ·1 , • ,. '.'. • •• ~., _ •. ' ' ... " • , •• " j"' -l~ I •. INTRODUC~IO~ . . 1 UCRL-ll404 .. The molecular-beam electric-re~onance (MBER) method of radio-frequency spectroscopy has proven to be very·l1seful in determining accurate values for the electric dipole moments.and nuclear hyperfine interaction constants of many of 1 2 6 127 .. , .-the alkali halides.' In t~e present work on Li I we have used the MBER / technique to determine the electri'c . dipole mOniefi.tf .. r;=th-e=Il~7 qiaa.Qa::,u:poJ.e..J.nter:--~--action eq~, and the 1127 spin-rotation interaction cI ' in the v=O and v=l vibra-tional states. The MBER method has also been used to study the J=l-7 J=O microwave transi-tion in Li6I 127. The microwave absorption spectra' of LiI have ;t>een observed :pre-vi9usly by Honig et al. 3 ,and by ~usk and Gordy. 4 Honig et al~ have reported '-~alues for the rotational consta.r:is, the 1127 quadru:pole constants and the. elec-t~ic dipole moment of Li7I. Rusk and Gordy report slightly different values of YOl and Be and they were also able to re:port a value},for De' The Yij~S refer -----to the co~fficients in the Dunham ex:pansion,5 and the other s~bols to the usual 6 band-s:pectra constants. In the :present work w,e obtained values for YOl and Bg which are in excellent agreement with t,he values of Rusk and Gordy.. Our di:pole moments are considerably larger than those re:ported by Honig et a1. .-:-II. EXPERIMENTAL A.. Technique -. The exper'imental apparatus used in this work:is the same as that used in . previous work7,8'on Li6Br and: Na.:F. The apparatus and techniqu.es used have been . 78 9 ' described elsewhere-',' and :will not be discussed here. 6 . ! 6 The Li I was prepared by dissolving 9;10 enriched Li in dist.illed water " and adding HI. The solution was evaporated and the LiI sample was dried in,a I -2- UCRL-11404 B .R~dio-FreqUenc~ Sp'ectra . . , The radio-frequency spectral lines observed. were produced by transitions of the, type' (J=l, mJ~O) ~ (J=l,mJ=±l) where J is the' rotational angular mom-• (A ' entum quantum number and m.r gives the projection of. J on the direction of the electric field., The J=l level, which is three-fold degenerate in the absence' of external fields !:ind nuclear hyperfine interactiOn)') is split into two levels , by the application of an electric field of 600.00 vOlts/am. The 1127 nucleus has a spin of 5/2 whic~ couples with the ~otational angular momentum through --' , nuclear electric quadrupole an~ spin-rotation interactions to split the J=l, , mJ=O level into 3 levels and the J=l, mJ=±l level into 6 levels'. It .was found that the spectra could be interpreted without the use of the nuclear hyperfine interactions arising from the Li6 nucleus which were expected to be much smaller . 127 than those of the I nucleus. The selection rules are ~=O, ±l, where IlJF =,mJ + m:r:::'Slr).d ~ is the projection. of the nuclear spin of 1127 on the electric field direction. These selection rules predict that 13 lines should be observed in the spectrum (see Fig. 1). Since~, eq~, and,cI, are functions of the internuclear distance, a separate set of spectral lines is expected for each vibrational state which is sufficiently populate'd. : In this. work a. complete v=Ospectrum and 5 lines of the v=l spectrum were obtained,where v is the vibrational quantum number. One line of the v=O spectrum is shown in Fig. 2. , { ( \;1 The full wid~h at half maximum of the spectrai lines was approxim'ately 4 , kc ~ This is consistent with the e,xpected uncertainty principle line' width con-sidering the average velocity of the molecules and the length of the transition . , .: ,'6' region, and a small broadening due to the unresolved Li quadrupole interaction • . . Thesignal-to.-noise ratio for the v=O spectrum was approximately 10 to 1. I , I . r '. I I .. ,.; -3- UCRL-11404 Spectra 'Were taken 'With both polariii;i;es"of the electric field so that .a I .t . --correction for a small contact potential that is present in the: Stark C~field , '4 circuit could be made. This correction amounted to 1 part in 10 of the line position. The reproducibility of the line maxima 'Was approximately 0.5 kc/sec. The principle source of error in these experiments is the uncertainty inth~ absolute value of the' electri~ field strength which amounts to ±l part in 104• The reproducibility of the field is an order of magnitude better than this and can be maintained constant to 'Within 1 part in 105 'While measuring relative 'Stark aplittings. C. Micro'Wave Spectr.a , 6' In obtaining the micro'Wave spectrum of Li I the C-field 'Was set at 50 vOlts/cm and the radio-frequency 'Was, set to produce the peak corresponding to Line 5 in Fig. 1. The micro'Wave frequency 'Was then s'Wept and a resonance 'W~s indicated by a decrease in the radio-frequency peak due to a depopulation' of the upper level by microwave transition, of the type J=l ~J=O. The decrease amounted to a more than 5Cf'/o reduction in the "flop-in" Stark' signal. . The observed micro-'Wave lines had a full 'Width at half maximum, of approximately 25 kc/sec. " ! . i -.. -4- UCRL-11404 " , ' . .! '.' III.· RESULTS AND ~:j:SCUSSION .1 . A. Radio-FrequencY'Spectra I The HamiJ,.ton1an necessary for interpreting the.spectra'of Li6I 127 is: J{. = B iJ..2 -.ll '.E. -eq~ 'Where B is the rotational constant and E is the electric field. - III fitting the spectra a .computer program 'Was us~d 'Which cal~ulatedthe matrix elements of ~ in a representation described by the quantum numbers'J, I, mi'~' The pro-gram diagonalized this matrix to give the energy eigenvalues. This program has been described in mor.e detail previOuSly~7 The unkno'Wn'input parameters to the program 'Were IJ., eq~, and cI • The program calculated the eigenvalues and . ,transition frequencies. corresponding to these parameters, 'Which 'Were adjusted until a best fit to the observed spectra 'Was obtained. The observed ,and pre-dicted lines are listed in Table I. The observed relative intensities given in the table are only accurate to ±2o% since the lines 'Were not all'taken at the same beam intensity. The molecular constants 'Which give a,best fit to the ~pec-tra are given in Table II along 'With earlier results. The ,:"alues obtained for eq~ are in agreement 'With previous results. In the present 'Work the experimental error has been reduced by 2 orders of magni-. . . . . tude. The spin-rotation constant,. cI' . is reported here for the first time. The present dipole moment fs higher than the previously reported value3 \ and is considerably outside of the combined experimental errors. Our dipole . ,.' .'. . 4 moments should be accurate to ±lpart in 10; the major source of error here being due to uncertainty in the electric field voltage. The precision or repro-ducibili ty of the dipolemom..e.t.tt.s: is nearly an order of magnitude better. Dis-crepancies bet'Ween dipole moments meagured by MBER and micro'Wave absorption ,. , .''; , r , • -5- , UCRL-11404 , i spectroscopy have been noted previously in' the .. case of LiBr3,7 and NaCl. 3,10 1 In all, three cases the .MBER value for the dipole moment is higher than the microwaveval'ue .. ,B. Microwave Spectra The observed micrbwave fre~uencies were corrected for Stark and nuclear hyperfine energies. The electric dipole moments and nuclear hyper fine constants obtained from the radio~fre~uency spectra were used in' making these corrections. Table III gives these corrections and the zero field fre~uencies, values of YOI and Yll we~e calculated from the e~uation '. v • o The Since we::'were able to measure the fre~uen<;ies in only the two lowest , . ' " 3 ,/ vibrational states, we used the value' 610 ±. 70o-ke/sec.".giY-~R_b~Ll,lQ!lig et al. for i . , _ • _ _.___.., _______ .. Y2l• The values for Dv were calculated , 4 from the results of Rusk and Gordy 7 ,6 for Li Br by making isotope corrections. Table IV lists the 1 f Y Y B, and B for Li6I 127 and com-va ues 0 01' 11' v e pares them with the values of Honig et ale Table .IV also compares the present results with the preyious values for Li71 using isotope corre~tions • '-... ! : , . ... '~~""- . : ..... -..... ~-....... -6- UCRL-11404 ; '. Table I.· Observed and predicted radio-frequensy ~ine positions for Li6I127 at . I , , an electric field of 6o~.00 voits/cm. ( , ............. " .. " . J=l ,v=O, J=l v=l ~"" Observed Observed Line Observed Predicted relative Line Observed Predicted relative No. (Me/sec) (Me.sec) intensity No. (Me/sec) (Me/sec) intensity • 1 18.5006 18.5006 100 1 18.8931 18.8932 30 / 2 28.3275 28.3276 70 3" 40.8378 40.8372 ' 70 3 42.1634 42.1639 20 4 41. 7682 41. 7680 40 5 47.6687 47.6683 40 6 48.5993 48.5991 40 6 50.2200 ' 50.2210, 33 7 49.0616 49.0621 60 7 50 . .8575 50.8569 .37 8 63.4503 63.4492 ", 80 9 71.3968 71.3989 90 ' 10 85.7859 ,85'.7858 70 10 89.0826 8~.0825 \ , 27 11 91. 7161 91. 7167 60 .. ,<: ~:-:;::~~--:""~-.-:---~.~:--.. -.. -' --~ .. , ":;~'-~----' -12 92.6151 92.6169 80 . ,-13 98.5488 . . 98.5478 70 ! ' i ' , ~ l c. r c. -7- UCRL-11404 Table II. Dipole moments, quadrupole-cou!'liI}g constants,c and spin-rotation constantS: oftLibI127. c Cc J..L CD) v=O v=l v=O v=l QI (ke/sec) v=O v=l Present· results' a 7.5l20)± 0.001 -198.780 ± 0.004 -207.453 ± 0.010 7.7 ± 0.4 7.8 ± 0.6 ~recision of the results is ±0.0002D. Previous results3 / 6.64 ± 0.20 -199.43' :!; 0.30 -206.8 ± 2.0 'c c" ·~c ___ • __ " r -8-. I Table III. Observed miqrowave transition. frequencies and corrections at 'E = 5~.00V/cm. Vibrational state o 1 Observed frequency V (Mc/sec) 30,637.8480±0.0071 30,336.312 ±0.014 . ! • '\ . / J=l and J=O Stark and hyper fine corrections (Mc/sec:) 28.2200±0.0030 29. 4457±0.0030 ... ' ........ ,,,.. ~. Zero fi~ld frequencies 'V (Mc/sec) o 30, 610.0235±0.010 30,306.866 ±0.017 .' " I '-~--::------'--~_-.-. . __ L._ ! -. -o-__ ~ ___ "._. __ ._ . __ ._._ . { . ! I I ti/ r .. • J -9- UCRL-1l404 Table IV. '.' Calculated microwave res1,llts. and comparisons. All constants arefin Me/sec. B e YOl -Y11(~C¥J Y21 (~e) Bo B1 Rusk and Gord; --' B 13,286.15 ±O.10 e - Y01 13,286.~62±0.07 -Yll (~c¥e) Y21 (Rrye) 4 Honig et a1. i5 ,381. 986±0. 08 15,381.448±o.08 152.59 ±0.10 0.610±O.070 13,286.785±0.08 13,286.386±0.08 122.62 ±O.10 0.455±O.50 Present results 15,381.013±O.10 --15,381.144±o.10 152. 799±O.15 15,304.895±O.005 15,153.316±0.009 13,286.110±O.10a 13,286.217±O.10a 122.670±O.15a . a....: 7 127 6 127 ' ~'or comparison with previous Li I results our Li I' measurements were corrected. for isotope effects • ',' ....• '~ . : ... '--, ... __ "_., ..... ~ ....... ~_,"., "~'" _ .......... '. __ n_. -10- UCRL-11404 . FOOTNOTES .AND REFp:RENCES r * Work done under the auspices of'the U. S. Atomic Energy Commission. 1. ·N. F. Ramsey, Molecular Beams (Clarendon Press, Oxford, England', 1956). 2. P. Kusch and V. W. Hughes, in Handbuch der Physik (Springe~-Verlag, Berlin, 1959), Vol. 37/1. 3. A. Honig, M. Mandel, M. L. Stitch, and C. H. Townes, Phys. Rev. 2£, 629 (1954) . 4. J. R. Rusk and W. Gordy, Phys. Rev. 127, 817 (1962) • .... . -- .. 5.' J. L. Dunham, Phys. Rev. 41, 721 (1932). 6~ G. Herzberg, Spectra of Diatomic Molecules (D. van Nostrand Book Company, " Princeton, New J~rsey, 1959)\ 7. A. J. Hebert, F. W. ,Breivogel, Jr., and K. Street, Jr., J. Chern. Phys. (to be published). , 8 .. ' C. D.Hollowell, A. J. Hebert, and,rK. Street, Jr., J. Chern. Phys.(to, be published). 9. A. Hebert, (Ph.D. Thesis) ,Lawrence Radiation Laboratory Report UCRL-10482, September 1962 (unpublished). 10. L. Peter Gold, (Ph.D. Thesis) ,Harvard University, Cambridge, Mass, November 1961 (unpublished). \ 1.: , ", I t, .' .I '. /, . \ \ . , . . , J \ \ -11-. .UCRL-11404 , '. FIGURE CAPTIONS '. 6 i ' . . ' 127 ' Fig •. 1... The energy. leveis ,of Li 'I , with respect to eilectric field strength •. The numbered vertical lines correspond to the· observed transitions between the indic~ted MF levels. MF = mJ + ~ • Fig. 2. 6 127 ' A typical v=O line for Li I atE =·600.00 V/cm.Th~s line cor-..... .' '. responds to line 4 (uncorrected' for contact potential) in Fig. l.The line maximum corresponds to a counting rate ,of. 6200 counts/sec over a background of .7000 counts/sec. . > ... .: ...... . '1.' ' .~ '. ' . .' .,.:,.' ,'., ' { .. : ..... " , A., I''>:' , ~, . '., .; . . j", ... '. . ;, - . :;.' '/' . :. .~ -" ->. .' :' ': . " '. ,. .(,,; '. ,i' " .. ~~ , .',', . ' . ".1 " ~ ',',' ':"'. . .... ', ;., .. , . . } . t "'" , , \ ; ',' ,.' ;. , ..... 1:,- '. , ~ . '. '. ~ ". ; .... " ...... . 't, """" ,.,,', " .... ~ ',,' , . . ~ '~,' ',' . , . "," ".,.'.' '·.f . /,' ,.':. ~, .. ,,,, .. ,',,' 100 90 80 70 60 50 - 40 u Q) 30 (/) "'- 20 u ~ 10 -0 >-CJ) 10 ~ Q) 20 c W 30 40 50 60 70 0 Li 6 1127 V = 0, J = I 200 -12 -400 Electric field Fig. 1 600 800 (V /cm) MUB-2849 fJ • \ . ,~ -en ...... c: ::s ~ t-o t-...... .a '-c -~ ...... . -tJ) c: Q) of-c: \.' LiS I Line 4 41.760 -13-.770 Frequency Fig. 2 .780 ( Mc /sec) 41. 790 MU8-3867 I " , \ 'J This report was prepared as an account of Government sponsored work. Neither the United Statesi nor the Com-mission, nor ~ny person acting oi behalf of the Commission: A. Makes any warranty or representation, ~xpressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, appa-ratus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any infor-mation, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any employee or contractor of the Com-mission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. 

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THE RADIO-FREQUENCY AND MICROWAVE SPECTRA OF Li6I127 BY THE MOLECULAR BEAM ELECTRIC RESONANCE METHOD

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THE RADIO-FREQUENCY AND MICROWAVE SPECTRA OF Li6I127 BY THE MOLECULAR BEAM ELECTRIC RESONANCE METHOD

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