Patel, M M

Rajan, K Jacob

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THE EMISSION SPECTRUM OF ZnBr IN THE VISIBLEREGIONM. M. PATEL AKD K. JACOB RAJANP hysics  D epartmepstt, M. S. U n iv e r s it y  o r  B aHoda ,B a ro d a , I n d ia .(Received March 23, 1967; Resubmitted January 20, 1968)(Plate 5)ABSTRACT. Tlie visible spectrum of ZiiBi* was reinvestigated in eniietion in the high froqiion(‘y discluvrgo. A system of bands degraded to red, designated as and occur­ring in the region \4r)50-~X3000 has been photographed with a medium quartz and plane grating M}>ectiv)grapl) liaving a dispersion of 7 A°/inm. The vibrational constants derived in tho analysis of this system are :=  135.80 ciu~i, <*>%■= 260.80 cm“ ,^-- O.lOcni-i, and =  1.54 cm“ .^1 N T K O D IT C T I O NTJie baud spectrum of ZnBr was first reported in emission by Wieland (1929) in the region A8470—A3300. Tho bands are dogradefl to the red and lie on a tiontinuuin wit!» pronounced intensity maximum at A8300. The measurements of about thirty band beads in the region A4500—A3600, which are weak in intensity and a general continuum covering them up, have been reported by Ramasastry el (d (1950) but no analysis has been presented so far. The ultra violet bands of ziiuc bromide wore known from the absorption study of Walter et al (1929). Howell (1943) examined those absorption bands and suggested a vibrational fre­quency of 220 cm~* for the lower state. However, ho himself doubted the data attributed to ZnBr molotjule as tho lower state frequency obtained is very nearly equal to tho well established ground state frequency of 223.4 cm~  ^ for tho Znl molociilo. llamasastry et al (1950) obtained tho red degraded ultra violet bands in emission and have analysed them into two component systems G and D of electronic transition with a ®I1 separation of 386 cm~*. They suggested 312 eiu~  ^and 318 cm“  ^as tho lower state frequencies for the two systems. In view of the inconsistonoy in tho above reported values for the vibrational constants of tho ground state o f tliis molooulo it was felt necessary to analyse the bands in tho visible region, and the present investigation was taken up. The results obtained are described here.141266126 M. if. Paid and K. Jacob MajanB X P E B I M B N T A I .Tlio Bpootrum of ZnBr was oxcitwl in a high frequency discharge from a 125 Watt oscillator working in the frequency range 10-15 Mc/Soc., using a pure sample of ziufi broniido in a pyrox discliargo tube of convontional typo. Continuous eva­cuation of tho tube with a high vacuum pump and strong heating with a burner wore necessary to maintain a characteristic white colour of the discharge. This condition was found to bo most suitable and for preliminary survey the spectra were photogiaphticl on a Hilgor medium quartz spectrograph. Tho final sjieotro- grams wtjro taken on a plane grating spectrograph with a dispersion of 7A/mm in the first order. Exposures of about 45 minutes wore found to be sufficient for obtaining satisfactory spectrograms using Ilford N40 process plates. Measure­ments of band heads were made on a comparator using iron arc lines as standard.K E S U n sTho baud spectrum of ZnBr recorded on a medium quartz spectrograph has boon reproduced in fig. 1(a) Avliich clearly reveals the nature and extent of the spectrum, The jdano grating spectrogram has beiui reproduced in fig. 1(b) as it appears on the photographic plate to bring out the finer details of the spaotruin. Tho bands are degraded to red and lino-Jiko structuro is observed in tho region A3850—A3750 The wave lengths of tho bands of ZuBr'^ ® along with their wave­numbers in vacuum, their visually estimated intensities and tho assignment of the vibrational (quantum numbers have been givem in table 1. The measurements of tho band heads reported by Ramasastry et al (1950) are given in column 3 of the table for comparison. In column 6 are included tho differences between the observed and calculated values of the wave numbers of the band heads.J) I 8 i) r  S S I O NThe bands obtained in tho present investigation are with fairly good definition and clarity and in addition to the thirty bands reported earlier sixty-nine more bands have boon measured. It was observed that the bands in the region A3900— A3750 were most intense an<l their intensities on either side docreaso slowly. For most of tho halides of this group of the periodic table it has been observed that the intensity distribution follows an open Condon parabola. It is therefore sugges­tive that tho bands in tho region may form tho apex of the parabola. Careful measurements of the bands in this region revealed that a decreasing separation ranging from 270 om~'^  to 255 cm""^  amongst the alternate members of this group exists. The progressions marked in fig. 1(b) wore first selected on this basis and a systematic analysis was then followed up.Tho appearance of the bands in tho region A3900—A3750 is misleading as it shows partial resolution of rotational structuro, Tho following reasons, how­ever, lead us to believe that it should bo treated as vibrational structure only.M. M. PATEL AND K. JACOB RAJAN Indian Journal of PhysicsVol 42 No. 2 PLATE - 514,07T JOn> 2=3 "O 0^J -1 (Utu 3ns. ^6, 1‘ N N =Ct> 07l/>■E. o£ Oo A-tpit r* rt 37.2=7 *-»W Z3To'V^ < rt U» 4,2o ^W (9 W "O=r A *2, O* 3 5,3-3700-3 7 5 0■3800-3 8 5 0-3 9 0 03950-4000-4 0 5 03600— 3800■40004200— 4400Emission Spectrum of ZnBr 1 2 7Table 1Wave lengths, wave numbers, intensity and vibrational assignments for the bands of ZnBr’ ®Wavelengthin AWave number in cm"*!Values of Kamasastry et alIntensity Asslgnnierit...... X^obs* *“ Veal*4227.5 23648 23034 6 1  ^ - 54206.0 23769 23780 6 # .5 04182.2 23904 23908 6 04161.3 24024 24029 6 :^»4 04158.9 24038 6 1^,5 04138.0 24169 24148 6 il,4 04117.3 24281 24280 6 |0,3 04114.9 24295 6 |2,4 24094.4 24417 6 |l.3 14093.3 24423 24422 6 3,4 - 34072. 1 24550 5 2,3 04070.7 24569 24660 6 ; 4,4 04049.9 24686 2409 J 7 3,3 I4028.5 24816 24819 7 4,3 04007.2 24948 24956 7 5,3 03986.5 25077 25008 8 4,2 03984.4 25091 3 20, 10 03966.0 25207 25207 8 5,2 _23946.6 25331 3 20,9 13945.4 26339 243.38 8 6,2 — 13027.7 25453 3 19,8 03926.3 25462 6 13,5 03925,4 25468 25477 7 7,2 _23910.2 25567 3 22,9 — 13909.5 25571 3 20,8 13908.3 25579 4 18,7 23907.3 25586 5 14,5 03906.2 26593 6 12,4 23905.3 25599 7 8,2 03904.5 25004 25608 8 6,1 13893.4 26077 2 25,10 — 13892.4 25684 3 23,9 — 13890.3 25698 3 19.7 03889.3 25704 5 17,6 03887.5 25716 6 1 3,4 03886.6 25722 7 11,3 03885.4 25730 25729 8 7,1 ~ 33874.9 25800 2 24,9 — 23873.6 25809 3 22,8 — 13871.1 25825 4 18,6 03869.9 25833 4 16,5 03868.7 25841 6 14,4 03867.6 25849 7 12,3 13866.6 25855 R 10,2 — 1128Table 1 {Gontd.)M . M . Patel and K . Jacob RajanWavo Wave Values oflongtli nimiber in Hainasastry liitens i t y Assignmoni -  Pad-la A et al3805.23864.13857.33856.23854.73853.33850.33848.93848.03840.13845.13838.63837.13835.63833.43831.93827.73825.93821.43819.33816.13814.33812.83810.43809.03807.33804.53802.63800.93798.53797.03794.73792.93791.03788.93781.63779.43776.93774.8 .3772.83770.73764.73757.5 3755.23762.5 3745.43743.03737.82586525872259182592525935259452596525974259802599326000260442605426064260792608926118261.302616126175261972621026220262362624626258262772629026302263192632926345263582637126385264362645226469264842040826513265552660626622266412669226708267462586625990261,30262572638526511266419 8,1 25 6,0 24 25,9 0.3 2.3,8 - 23 21,7 - 23 19,6 - 1G 15,4 07 13,3 09 1 1,2 - 39 9,1 I6 7 0 03 24,8 03 22,7 — 13 20 6^ - 24 1 8,5 25 16,4 T10 10,1 - 19 8,0 06 25,8 14 23.7 34 1 0,5 05 17,4 06 15,37 1.3,2 110 11,1 09 9,0 06 26,8 25 24.7 14 22,6 - 14 20,5 25 18,4 - 25 16,3 08 14,2 ~ 19 12,1 - 19 10,0 - 14 21,5 05 19,4 06 17,3 26 15,2 18 13,1 08 11,0 03 22,5 16 16,2 07 14,1 07 12.0 23 21,4 I4 19,3 - 14 15,1 0Emission Spectrum of ZnBrTable 1 {Contd.)129WavolojigMiin A3735.03723.5 3720.73717.53704.0 3700.93084.1 3607.0W«.vt>mimbnr iii cm*'*207002084920809208922099027013271.3027258V^ uhios oTlltLiiuiHnst ry et al2070020S9027027271,3027264Ini onsH y A .K s ig n in n iit  {V ', V")13.0 18,210.114.017.1 15^ 0 10,0 17,0VfflrZ*1002-1000Table 2Vibrational isotopic shift in ZnBr baiwjsAssignment i-r' , r")Observed Shift- TJioorotical shiftiri em*"* ?n cm*"i17,0 1 1 i 110,0 JO to15,0 10 917,1 10 914,0 9 810,1 9 918,2 9 91.3,0 9 1019,3 8 812,0 8 911,0 7 710,0 7 0(i) Rotational structure of heavy molecules like the one under investigation could not bo resolved under the resolution usefl.(ii) Under the moderate dispoision used in the present case the vibrational bands of one sequence may overlap with those of others.The line-liko structure could then be explainotl by assigning them the ap­propriate values of (»', v").Following the usual procedure (Herzberg, 1950) the vibrational constants of the molecule were determined and the following vibrational quantum formula, which accounts in a satisfactory manner for all the observed bands, was derived.= 26138.7+[135.80(v'+l/2)-0.40(«'-f l/2)»] -[269.80(u'-fl/2)-1.54(v*+l/2)*]130 i f .  M. Patel and K, Jacob RajanAh tho abuudanoo ratio of the two isotojws of bromine (Br'^ * and Br*^) is nearly o<(iial oiKi may oxiwct tho intensities of tho corresponding isotopic bands to be nearly the same. Tho isotopic separations for tlvo loss abundant molecule Z n B r" liave l)oon calculated using tho formula :v,_v =  (yf)-l)[«>'+l/2)-to'>'’+ l/2)]-Some of tlio hands for which tho isotopic separatiem is appreciable have been shown in table 2. The isotopic separations for tho bands in the longer w ave-len gth  region are less than 5 cm~^ which may account for tho diffuse nature of the bands in that region.Tho spectrum of this molecule in tho near ultra-violet region has also been studied (Rajan, 1967) and a frequency of about 271 cm~^ is obtained for the lower state which is in good agreement with tho value obtained in tho present investigation.For the zinc bromide molecule the low lying state belongs to tho electronic configuration ‘ and in all probability is the ground state. Tlie upperolectroni(! state can not be specified precisely though in all probability the transi­tion may be rr^ oTr^ tr®, ^2+ (ground), involving a transition o f thoelectron from an inner (t to the outer a orbit, which is consistent with the observed decrease in the vibrational frequency of tho red degraded bands of tho system.A C T v N O W b E D G E M E N T STho autliors w'ish to express thoir thanks to Professor N . S. Pandya for his keen interest and encouragement during tho progress of the work. One o f them  (K .J .R .) is grateful to the O .S.I.R . (New Dellii) for tlie award o f a Jr. Research Pellow.ship.II E F K K E N C E SHoi'.'/.borft, (}., lOrtfl, Molecular Spectra and Molecular Structure. 1. Sj)ec.tra of Ih'atomic Molec.nlcx (Van Kostrand Co., ’Now York)HoWoll, H. (}., 194.*). Proc. Royal Soc., 182. l^>.Kajan, Jacob, K., 1067, Pli.F). Thesis, Thu Maharaja Sayujirao UniverKity of Parcda. Raraasastry, C. and Sroeraniainnrthy, K., 1950, Proc. Nat. Inst. Sei. India, 16, .S05. Waller, J. M. and Harr.vil, S., 1929, Proc. Royal Soc., 122, 201.Wieland, K., 1929, Heh. Phys. Acta, 2, 46.

The Emission Spectrum of ZnBr in the Visible Region

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The Emission Spectrum of ZnBr in the Visible Region

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