The H. F. emission spectrum of cadmium bromide molecule is reinvestigated P, Q component head splitting is presented for the (o, o) and (1, 1) bands of the main system and a few additional bands are assigned to this system. A new group of bands is interpreted as forming the Counterpart of the main  system which arises from 2 π-2 Σ transition. About 50 bands arc measured in the visible region and regularities shown

Ramasastry, C

English

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61BAND SPECTRUM OF CADMIUM BROMIDEBy C. RAMASASTRY(Received /or publtcalion, Rcb. 15,Plates X X IIA  aud B#ABSTRACT. 'J'he H. F. emission spectruin of caamiiini bromide molecule i.s rein­vestigated r , rompmieiit head splitting i.s presented for the ((j, o) and (1, 1) bands of the mam sy,steni and a few additional bands are as.sigued to this system. \ new group of bands is interpreted as forming the rounterpart of the niiin .sjstem wliieli arises from *n - - 2  transition. About 50 band.s arc measured in the visible region and legularities shown.1 N T R O D U C T I O NIn llie early work of Walter and Bairalt (1929) on the absorption spectra associated with various compounds of zinc, cadmium and tnercury, about 12 bands were listed in the region A3551 to A3407 as belonging to (Cd+ Br). But the wavelength.s of rhe.se hands agree closely with the TlBr absorption band heads obtained later by Butkow (1931) and so the bands are considered by Pearse and Caydon (1941) as really belonging to TlBr but not to Cd Br. Recent investigations of Oe.ser *^ 1935) b^e absorption and fluorescent spectra of the halides of zinc and cadiniurn did not reveal any discrete bands of the CdBr molecule. The liigh frequency emission spectrum of cadmium bromide vapour was studied liy Wiclaud (1929) who analysed a system of violet degraded bands of high intensity, lying in the region AA3250-3120, as consisting of six sequences with the (0, 0) liand placed at A3i76!65, ' ' 31470-5 ' He also listed three unclassified bands at A3395.i(3), 3092.5(1), 3075.4(0). The existence of difluse bands in the visible region from A640o~ A3300 was just mentioned by him but no measurements were given. Howell (1943) considered, from an analogy with tl,ie band systems of the other halide molecules of Zn, Cd, and Hg, that the system analysed by Wieland should be one of the components of 'IT -  '2  transition ; but the other component system could not be established. The present work is taken up with a view to finding out this missing component system and to search for other band systems of CdBr which would coi'i‘es))ond to the various known systems of the related molecules.e x p e r i m e n t a lThe discharge tube is of thick-walled pyrex glass with external elec­trodes, the source of excitation being a H. F. oscillator constructed by the454 C .  R a m a s a s t r yaullioi. Heating is done l>y an clna Imnic-r until the colom- of the dischar.qe IjccoiiiL's intense vvhilL'. Ilfovd Selo elirome and vSpeeial rai)id plates are employed for ])holoL;rai)bin.L; tlie lirmds PiLlnninary investi;:^ation is earried out U'itli ITil.eer ^inal! and meiliiini cpuiri/ s[)ertro^>raplis iisiii'i i>lnlcs sensitised for tile far ultra-violet.K  S  TT  I .  T  S(a) No bands aie fiblained in the re^eion A3000™A r(S5o but foui broad and ill-defined contirimi are recorded exluubn.e ovei regions (/) ^55<’HI) AA,.>6to (Hi) and (rr) AA.,\S75 — :jg3n.(h) The visdde bands, clearly red-dee,raded, occur in llie legioii A,j(.)(_)u — A^ K^ So Mf tliese, those lyin.e between A4.ion Aincfo aie of greater intensity than the rest There is alsf) a sliong genu  al L ontinnnni ovei lying the visibjle bands* 'i'liis conhinuini ...ladnally fades away 10 shortu wa\’eleiigllis and s^ practically iinperce])!ible at abfiut A44^0,(r) An isolated violet degiaded band at A^ jc)!^  i and anothei iainl bamt\ at obviously related to the former, could be definitely ol)served.Id) 'riiL Wieland system (naans in the iegit)ii Ai;23o — A3100. This consists of the most intense Ijands of the entire' siiectriim.(e\ A few faint bands in tlie A3oc)o legion could lie detected in the lotational structure of the ( )H band, A3o(),i.*v S V S T P M  nWielaiubs system (system 7^) is pliolograi>hed by the author on the liilger qnaiiz Litlrow' spec lrograi)h. Tighter exposnics showed tliat tlie (o, ol ancl (i, i) bands are split nj) into two component lieacls (Plate- X XIIA , [''ig. a). Such double heads aia- not observed lor any ol the remaining bands of the system. JTcnce the alnive components cannoi lie due to bromine isotu])e effect but aie to be considered as P and Q heads Details of niea&nrenieiUs arc given belo\v :TAllUi 1A a")1t' W0, n i1 r.'cg%1, 1 .P VVv)Band Spectrum of Cadmium Bromide 455i h c  number of componenl heads observed hi each liaiid i;ivcs the conclusive evidence for tlie consideration that the system is due 1 o " H  --*!£ transition. 1  hen the other component system should also be pres iit, from the analoiLiy of the spectra of the correspoiuHn.e, molec'ulcs. 'i‘lie three unclassified liands of Wielaiid ni the A3005 region cannot fonn the inissin.e, component system, for (/) they K^ *ve cm'"  ^ bir the ' 11 w idlli which is loo small compared with the expected value of r T p) c u r   ^ clenh ed from the ' P  set)aratioii of the Cd atom iii] there are no rei’ iilarities anioiiy the bands In llie leepon of tliese iaint bands listed l)y Wieiand, a few more bands also could be iiieasuivd in the present work ; the [jreseiice of a band is suspecvLd wherever there is a shading of the rotational lines cd’ tin, ( )1T band (Idate X X I I A ,  Fi.e- fO. This [rai;mentar3^ iU'oni) can \ki interpreted as fonnlnp; the higher members of the Wieiand system and the bands are classified acc^mdingly in 'Table 11.TAinjc  IIAdditional Bands in llie D-svstem of CdBrW R ' P m d  : A u I I k 'I{ v \  v " \A ( I j l l . )  1 A ( 'Ji lt ) /'nlif I'CllI( 3 ) .) ' S "  J 3 "  ’ 0 0  3j g  ^ j '1 ; S C 'l ’ . 3  3 3 1 ■ ‘ ' l l ,  ' 1 ); o S ( )  (( i j 3 ■ i  -0 Ol. V- 7 S  T ' ' i  1 S-'  ^ " 3 >^uS S h ,  2 1 ^ 1 3  ’ 0 . 1 17 .  3 I- 3  1 V  1 ( S ,3 ’ v ; ;  ] t O ) ,  h /■ m )1* u  7>|. l  ( m ) 3 3 ^ t i j ,  ( d1The [lositions ol the vaiions bands is calculated witli the I k  Ip o f  tlie formula3 1 4 5 ^ , 3  I a 34 5 b / ' + - A  “  2 3 o . ( j ( m ' M - i )0 . 7 3 ( / / '  1 2 ) '  +  o . 3 o ( / / ' ^  I !t)'‘whitdi was dc-rived l)y Wieiand fitietj) \o represent the 7)“Systein. 1 he above Ixmds form a continuation cd* tlie intensity parnbol.i when arranged i n  a Devslaiulre's tahles thus supporting tJjeir jaositions in llie viliratioiuil scheme.S  Y  ' 1'  1 :  I M  rW i t h  the  l ia n d s  on  th e  s h o i t  w a v e l e n g t h  s ide  o f  th e  7 7 -systeiii  l ia v in g  ;jeen c la ss if ied  as a b o v e ,  th e  o n ly  a l t e r n a t iv e  le f t  is to  id e n t i fy  th e  t w o456 C. Ramasastryisolated bands at A3208.1 <3) and 33237  ( i ) as the oilier comijoncnt of thedoublet sysleni - " 2 . These bands are shown in Plate X X I I B ,  Fij;. c .  A s  is expected from what is found in the rorrespundin^ band systems of CelCl and Cd l, this system is Ira.enientary and occuis on the long wavelength side ol the tully develoi)ed c:ounter[)art component analysed by W ieland. Tile bands are arranged as hereunder g iv in g  a h)\vei‘ state first diGeience of 23/] u iiils wliich eomparcs well with the ground state vibrational frequency uf 230 units u liich  is established from the analysis of the D-systeni.T A llU i I I IC-system of CdU r Bands ^ I hoI h ir th e r ,  th e  se p a ra t io n  b e h v e e n  th e  (0,0) b a n d  o f  th is  s y s te m  a n d  th a t  of  th e  n-'System  is 3 147 0  — 3 0 3 1 2 ~  11 5 8  e n n “  ^ w h ic h  is in s u c h  e x c e l l e n t  a g r e e m e n t  w ith  th e  j jred icted  1 1 jo u n it s  tl ia t  one c an  c o n f id e n t ly  c o n s id e r  th e  m is s in g  c o m p o n e n t  o f  t lie  tran sit io n  as e s tab lis l ie d .AM S J n h K S Y S T K MIn none ol the investigations on tlie spectrum of the C dB r molecule are measurements available for the 1)nnds in the visible regiom In  the present wairk, tliese bands are iihotographed on a I'ue ss glass spectrograpln A t  higher dispersions the band heads l)ecamc diffuse. Wavelengths, visual estimates ol intensities and waveiuiiiilier data of aliout 50 bands are given 111 Tabic IV .Plate X X I I B ,  F ig . shows an enlargement of tlie I'uess spectrogram. The bands are clearly red degraded. Tlie heads are single. They are almost a iun lly  spaced. The separation oi bands is about i io c m M ^ .  A ssum ing  that the lower state of the visible liands of C dB r is identical m \ h  its ground state (u )/-23oC  these bands can be arranged into long progressions. Fgicli progres­sion consists of alternate bands and gi\x\s a first difference of about 220 cm.“  ^for the lower state. Tliesc regularities are show’ll in T'alde V. If  the scheme is correct, there is jiredissociation in the up[»er state at v '  — 2 .g e t ' l l .«r t ' I IT I / . V K( v ' O( o ' o )To'd) -'iK'.-.'-( 1III-1. . . . . -  o(MrOU4HCV-Jt:-PQr )ar:fT>GUJPiH00<oo<<Pi*.■T3X<CL,>->ck;Hoo<CO<<P iBand Spectrum of Cadmium Bromide 457392«'i3944'3396:1.43978 4T able IVCdBr Visil)lc BandsTnt.S^3'164355-443/6->1308,14418-5lilt*2054JJS44'^ 273123 90 7 -3 2 4438.0 ! 1 2252-'.4013. fS 4461 7 , 1 2.rin';n 2 100X4 184-" 4 2229.S10313.63 2 1803 4 S'M-4 5 221  CM,1n|8.^  i 2 2 16044o()7 2 4525 6 .:2of)(»24,58'-' 1548.4 5 2 ) 0 7 0; 1 -rn6o 4570.4 5 218744103,2 i 3 21361 459 4 -5 4 217584 1 U .4 1 212374130.8-1613 i) 3 21668-1 2414^) 46ir).n 3 2 i 6 .r-]■ U 5 ^ 7I4 ! V\3 0 4638.0 3 3155.51 1643 ' 3 2 1 5 3 141756 1 6 239424 E )5 9 3 238^ 6 .'l66>.n ' 3 21444i 46S0.4i213)01214.:’- 4 I 2 3 7 2 .-A4 2 .34-5 4 I 2 36of) 4712.4 212 7 51254-8 1 3 ' 23496) 4 7 3 3 -5 1 211204274.2 1 3 i 23300 4 7 5 7 - 5 j 1 2 1 ( 0 44204.7 I 3 j1 23278 4 7 8 2 . T 1 1 2000514306.7 1 3 : 2321.3 4807.0 1 207934 3 T5 -'» : 3 23168 4831.0 J 206914 3 3 5 -8  ; 2 23037K L E C T K O N I C S r  A T E S.Four band systems arc cstablisht’d in the case of each one of the molecules CdCl and CdT, one in the visible, two in the ultraviolet and one in the far ultraviolet. [Wieland 11929), Howell (1943), Raiiiasastry and Rao (1946), Rarnasastry (1947)]. rhere is good evidence to consider the two near u.v. systems as due to * I J ' ii transitioin The visible system, how ever, is probably due to ti ansition. Tlie corresponding systems ofCdBr also can be interjireted accordingly. The lar u.v. system of CdCl and Cdl have their (0,0) bands at A2205 and A23S7 ies))ectively. But in the case of CdBr no such band systeni is obtained in region of the emissionspectrum excepting a continuum from A2550“-A2500. If, in spite of the disagreement in the region of occurrence, this continuum is supposed to correspond to the far u.v. systems of CdCl and Cdl, the difficulty still remains because this upjicr state of CdBr is repulsive giving rise to continuum . 5-“i7i2r‘—10458 C, Ramasastryinstead of bciiift stable as in CdCl and Cdl molecules. In CdF also (Rochester and Olsson, 1939) tbc corresponding system is not observed Imt this region of the CdF spectrum is not yet systematically investigated owing to experimental difficulties and in all probability a band syteiii of CdF should exist round about A2T00. On analogy with Zn halides (Ramasastry, 11)48) one more band system is to be expected for cadmium halides also between tile far ultra violet and “TI — " 2  systems. But no definite evidence is as yet available as regards their existence, though about twenty diffuse bands are observed in tlie expected region (author's unpublished woih on Cdl). Probably the level is repulsive in Cd halides and one of the observed near n.v. emission continna of CdBr may iis well be due to such an unstable level of this molecule.A C K  N O W Iv F  n  M  K  N TThe author is grateful to Prof. K* R. Rao, for his kind interest in t]\e work.R F  h P  R IC N  C F vSBntkow, Tq^ T, ZHis,  V\ Pliys., 71, qyS.Howell,  iq/]3, Prnc. Roy. Sne, A182, qs.Ocser, 1Q35, Zcils.  f /*//v ' s 9 S. fiqq.iVarse anrl GaVflon, iq]t,  TdenlirM'al ion nf Molrciilnr vS])ertrn, pq Rnniasastry, io47, /c/o. /'//ys., 21, .Ramasastry,  iq.l8, /ad. Join Phy^ r^i, 22, lU)Ramasastry i;nd K.R.Rnu,  ig4(\ hid.  four. Phys.,  20 , mo. Rorhest. j  and Olsson, ni3q, Zcils.  f. Phys.^ 114, ,[05,Walter and Unrratt, u)M), Pnjr.  Roy. Sot , A122., jor Wielnnrl, iq 'q, TTcIv. PJiy. /I f , 2, jO iS: -7.

Band Spectrum of Cadmium Bromide

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Band Spectrum of Cadmium Bromide

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