Ramasastry, C

Rao, K R

English

IACS Institutional Repository

ULTRAVIOLET BAND SYSTEMS OF THE MERCURY IODIDE MOLECULE. PART 111Bv C. RAM.\SASTKY Asi. K. R. RAO ‘(Hrcri i ' i ' i l  lo} [^nbrnatiojif lu>ic o, u//y)(Platu V)ABSTRACT. Tlir band spiTtnini of thr.* infiniry indidr bas been inveslij;oledfurtJier in the nllra viidet in tlu' rt'jL^ ion beUvmi A 2411,) -  as excited !>y a specifdlyconstriutcd bij;;li IrcijnencN (iscillator. The G and II systems an' cnnsidcrably extended ; tb(' (^system is analysed for llie first time and a new vibrational scheme is su^ ^^ f*csted for the IP  system, diffcTtnt from that projiosed I>y Piidieshi je\\a The vibrational Ci)nstanls are16(j-systeiii ... 88.4 0.2 1 5^*7 1.2ri-syslcni ... 97-1 1 125.3 1.15Ae 7f’t”The tvN’o systems liave a coninmn final level whicli is the same as tliat f^r the C and D svslem‘‘. I l l  the TT-system, tlie progressions are <abrupny eut olf a f t e r ; thift Is cons­idered as an instance of predissociation m^ t found in any oi the syvStems of the merenry hali­des EO far analysed,I N T R 0  T) II C T I O NI'lie emission spectrum of the mercury iodide molecule was {omul to con­sist of seven band systems in the region AA 44oo‘-2ioo as listed by Rao, vSastry and Krishnaiiiurty (1944) in Part I of tlicse papeis which contains a review of the work done by previous investigators on these bands. The systems were de­signated as B, C, D, E, F , G, and H in the order of decreasing wavelength, the H system occurring at the most refrangible end of the spcclinm. Iliiee more systems, were later discovered by Ramkrishna Rao and K. R. Rao U9 4 0  and described in Part I I ; they lie in the region between the F and G systems and hence designated as F „  F , and F.,. The systems B. C, I), and K are extensive, each consisting of quite a large number of bauds, while the others extend over shorter regions and are somewhat fragmentary. Vibral’onal analysis was sug­gested only for C and D and F, and F „  all oi which were shown to have a common lower state, probably the ground state of the molecule with the approxi­mate vibrational constants ug = 12 5 .2  and =  it was shown further that the two systems C and D whose (0,0) bauds have a wavenumber separation of 3510 cm-’ might form the components of the electronic transitionanalogous to similar systems established by Howell (1943) in the HgF bandsand by Rao and Ramchandra Rao {1944) in if^kCI bands. ^ T>l)ow of the Indian Physical Society144 C. Ramasastry and K. R. RaoWitli a view lo llie ulnrirlation of the entire band system of the Hg I niole- enle, liirlher woik is carried out and in this part, the rCvSnlts relating' to the G and II sysLeiiis will be dcscribecb When the slruclure of the entire band sys­tems is completely known, it would be of interest to examine why many sys­tems are emitted by tliis nr.'lL-cule wliile only a few are known to exist in each of the corresponding molecules llgh\ HgCl and HgBr, UvS well as in the halides of the othor elements, zinc ami cadmium of the same periodic group. It is hoped that some of the ten chaiaeterisiic systems of Ilg  I might prove to be iiilercombinalioii bands due to transitions between excited states of the molecule,/T-: X I ‘ K k  1 M p  N T A I; !A ])uie sample of mercniy iodide is taken in a thin-walled jiyrex ti^hc about 8^ ' long and ball-imdi internal diamelei. Idie tube is continnou^ly evacuated by a Ceiieo llyvae j)um]> and excited by a radio frequency voltagfe, available at the ends of Ihc' taidv circuit of a llarlley shunt-fed valve oscillator of j to TO Mega cycle s range, 'rhe heat of the discharge is sufficient to vapo­rise the mercury iodide in the Inbe. Within a minute of switching on the oscillator, the coloui of the discliarge turns intense blm*, characteristic of the Ilg  I vapour. 'Idle spectrum is idiolographcd liy a Hilger Quartz U 315 si^ectrograph, using an exceedingly narrow slit Tin's narrow wddtljhas proved to he wairllnvlule in lesolving some close band lieads, in spile of their general dill used nature. Ilford Special Rapid plates sensitised by high grade mobil oil served wxdl lo photograiili the spectrum below Aj3oo. Zenith ' 1-ast Ultra- Violet plates ol high speed and Ilford plale.-s type Q III aie also employed. Ux[»osures of even two horns duration gave very good spectra. d‘he copper arc {standards are adopted for reducing the plates.As pointed out in Tart II, in view of the jieculiarly large numbei of sys­tems attiibulcd to Hg I molecule, special care is taken to establish first, as far as possible, from an experimental standpoint tlic origin of these band systems and to examine that they arc not due to other molecules or to the products of dissociation of mercury iodide. Comparison is made with spectra obtained under identical experimental conditions of various other halides and chifley iodides. I he band spectra of the tw’o molecules, mercury and iodine, have also been studied in detail in tliis respect* There is evidence on the plates of bands attiibulable io Hg^ and Hg.  ^ but they occur in regions remote from that t:)f (1 and II systL'ins. ^\s iodine is known to Ixive an extensive band system observed in absorption and in emissiou below A 3500 down to the vacuum ultra­violet, plates have bt^ eii taken wdth iodine alone in the discharge tube and the data arc compaied with the bauds ascribed^lo iodine by the ]»rcvious investiga­tors, Curtis and Kvaiis (1033), Warren fio35), Venkateswgudu (1946). It is found th.il undei the coudilioim adopted in our expcrimeiils no trace of iodine omissi(m bands appeared in the region where the G and II systems of H gl occur.( )n the olhei hand, a general continuous spectrum is obtained extending downSASTRY a n d  RAOPLATK V2W-J44^-i(\ i')'/jI f’:ai a)  G System with Culture. i/j) H System Comparison.to X 2000. It might bo maatioued here lliat this iodine II. 1 '. ilischargc could as well be employed as a source of ooulinuous specUami in Die ultra-violet absorption experiments in place of the usual hydrogen discharge lube. Such a source has, in fact, proved very easy to set up and convenient to work with and is being employed in our laboratory with success. j\ full description of this will be found elsewhere. The above exi)eiimenis have led tlic authors to con­sider the mercury iodide molecule as tlie emitter of the T. and H systems, A further confirmation is afforded by the vibrational analysis of the two sys­tems suggested in the succeeding scclit)ns.R K STfLTSG System.—This system, lying between /\A —2165, was first reportedby Prilheshejewa (1032) wlio piiblislied meavSnrements of 22 band heads which were from a low dispersion spectrogram in which the individual nieinlicrs of tlie sequences could not obviously have lK‘eii snlficieutly resolved, l^vcu the dir­ection of degradation of the liands was not deliiiitcly observed. No analysis or regularities were suggested liiiii. In the present work the dispersion used is about 5 A. II, per iiun. in this region » a much laigci nunibei of band heads, about fifty in all,, are measured. They are found to be clearly led- degraded with sharp heads towards the violet side- A icpioductiun of this system is given in Plate IV  which is a four-hour cxposiuc with copper uie com­parison.The wave-lengths, intensities and wave-numbers of the Irand heads are given in Table I. The intensities are visual cstiiiuitevS. For comparison, the data reported by Prilheshejewa are also given iirtlie first colunin. The analysis of the system is found to be comparatively easy us Ibe heads are characteristically prominent and fairly resolved.I'Anuc Illaml heads of the G-vSystem.UltraOiolet Band Systems of the Mercury Iodide Molecule 145Wave lengthPrlllieshejewa2239-72234.602227.2Authors3234.3n 2233-Sf’ 223;'. 60 2231.61 222K) 22 222«^ .222227.372226.202225.212221.ITill. Wave imnilici (UassiTiai-jij(lull; n 44742-7T 4475'"'-7; 1 447/6-7 "2 8)3 44796.7 (J.7)1 II 4 |«44 (4,914 lS6 po2 44M<S2.(» f2 ,7  ^ >: 3 449^>37 (1,6)1 <■> 449-5 6 . (0 .5)i 44960.0 i  l'^7)11 2 44992.9 1 (2,6)a— 4146T able I ( c o n t d . )Band heads of the G-system.C. Ramasastry and K. R, RaoWave lengthInt. Wove numberilheshtjewa AuthorsJ25220-3j2220,7/1 ! 4 45016.02219.38 i 3 451>43-62218,71 1 0 4.5057-22215.02 1 A 45132-22213.3 2213.61 5 4516J.02212.0S 2 45193-22 2 11 .17 I 45310 82210.86 0 45219.622og 12 I 45252.72208.D 2207.78 6 45280.22207.03 0 45295-62205.0 22(\S.I2 113 45334-8220/|,6 2203.63 A 45365-52202.56 ! 4.5.387.52202.4 2201.92 A 4,5400.72201.00 2 4.5419-72199.59 2 45448.72196.0 2197.67 6 45488.42196.24 0 45518.12195.12 4 45.541.321933 3193.53 4 45574-32192.50 3 45595-73 19 15 2191.72 4 45611 93190.0 2190.94 2 45628.12189.67 1 45654-62188.45 3 45680.13 lSS ,3 2187.55 6 4569S.82187.01 0 45710-13185.3 21S5.63 I 45739-12184.23 0 45768.42183.5 2183 36 5 45786.52181.02 3 4583572I80.7 2179.33 5 45871-32178.64 0 45886.72176.80 3 45924-62175.0 2 17 5 13 4 45959-82174-44 I 45974.32 17 37 5 1 45988.92172.69 3 46011.42171 4 2171.06 2 46046.92170.49 I 46058.12169.68 0 46075.22168.5 216S.76 I 46094.82168.0 2168.05 0 46109.82167.16 0 46128.82166,60 00 46140.72165.99 0 46153 7Classlflca-tion(i.S)(0,4)fa.i)(5.3)(1.0)(4.2)(3.1)(6.3)(a.o)(5.2)(4.1)(7.3)(3.0)(5.1)(4.0) (7’2)(6.1)IS.01(8.3)(6.0)(9.3)(8,1)(7.0)Ultraviolet Band Systems of the Mercury Iodide Molecule 147,tows4-*K  6H-lUS o« .2aCQa.2OJ>I'C.CO-TCOtoVDC/JVOgOv 00vdoo'nooVOs00oO3"r»O 'T?■rrM "oGOCO‘nC’S.■^ rr fr roc>?//  >:»so rt- I- VD ICXI'bs  ^vds. sVO o  lo ^  3v OvDrOZt-4'Oj:) 3lOCO H4 3 * tT 3 fO oo 3 CO i >- 3 MMVDM•o-*1-ClU)t'jCOr f'rt-r*-itoCOTTdvM■rr•o■crcdOVCO ;§LOst--»oVO'S 3 3 3 CM 5 p M/-•c'»b r>^ 't o M IM "To M< «c»lOCOVOmlOcd?■COMlTTCOcy-jcd\oWjdMt'*LOCOgglO■crO 'OcLOTcrcdlOoVO'<r3~-r M "m /O JO JOto v5 M CO8CO■<rcd60t T>o'?rr rCn.lOCO’ccj-•d"*ovO»o□>TOCOidtoooCO*0-r ro .itjM n-vOMJ--_ --- . . . — - - - -  -- -'-- 't oCO'p-jto33_o«JMVOCOTj*• o W 1M 1 ».OOCOn -cdCOO'COvd ooCMVDO hi w CO tO c/5 Ovt ’tnleyoi-^Vul•^gncC'CTT?'£jr•^3 CT& 9U9'ociI'^CJJ48 C. Ramasastry and K. R. RaoTAlil.K III.'1()625/17ns, 8 /]l2b2■ iHgg 46:262Table II presents the baiuls in the usual diagonal airay. It will be seen that most of Ihc intense bands fall into the pro.erc*ssiun with v ' - o  andW'  ^pro.e.ressioiis with and 1 ;  the intensity distribution is such that the Fraiik- Condon jjarabola is very wide and ojien, tiie (0,0) band being absent- 'J'he values arc not, in spile of the sharinicss of the band heads, very rcgulai ;^ but the general scheme is bebeved to be correct. The following vibrational formula is calculated for the bands by plotting the AG(7') values against the quantum numbers and adopting the graphical method.™ /I5542.4-1-(SS.4 If/—o.2u '^ )—fi25-7 wheie =  i) etc.The values 125.7 and 1.2 indicate that the lower .state of this system is the same as that detcrmiiied previously for the C and 1) systems.H-S3cs‘/cm.—This system too was first reiiorted by Prilheshejewa but the nuinl)cr of bands was only ten. The scheme in '1‘able Ilf was also tentatively suggested by the above author, which, according to the present Work, appears to be very fragmentary and uncertain. vSeveral bands reported as single by Prilheshejewa are oliserved to consist of blends of two or more heads and hence an altogether dillereiit vibrational analysis has been obtained. The new scheme is i>resented in 'bablc IV and 1 able V gives the details of the measurements. Twenty-two baud heads are measured between 2170-21 lo* The degradation of the bands, as can be seen from the reiiroduction, Plate IV is definitely towards the red as in the G-System. This feature suggested the rearrangement of the heads shown in 'J able IV, which leads to a value of 7c/ <  7C'/', while the Prilheshejewa's scheme gives a-/>  re,/' unusual for red-degraded bands. Further, if Prilheshejewa’s analysis is adoped, many of the strong bands would be left out of the scheme. With our analysis all the bands can be represented by the formula,i- = 47iio.2 + (07.1 —(125.3 n/ -^1.15 w"“)'Hie AG(i’") values for this system are much more regular than those for the G-systeni and the constants calculated for the lower slate arc considered as accurate. For the upper stale the constants are derived from only two AG(d') values-mtraVioUt Band Systems of the Mercury Iodide Molecule 149<5(>15NOOOnVOV.O',C*-1Cb^iga>-4-«(/]wwH-r<UiincdnG313a.2'-H3cdUi•oONi^*j□f.riNO'inCOvO^  VOs'rr\oo-  a150 C. Ramasastry and K, R. RaoT abi,e VBand heads of the H-syslem.Wave Nil 111 herWave length lilt. Classifica­Authors Prilhesliejewation2161.15 3 46257.1 46262 (3.9146271,8 (i.H)2156.20 A 46565.32 l.SS-4ti 3 46378.1; 46382 •1.7)2I54.SI 1 46393-2 (0,6)^I.SI.27 4 46469 5 ( i 7)2150.43 5 464S7.7 (i,6)2140.61 3 46505-4 46499 u>ls)2145.20 4 1146601.0Ifi.i)\fo,4')5 i 46619.S 466252141.35 tK) 46684.8 <2,si2140,07 0 46712.7 ' 1 .4 )2139.02 6 4673.'!-5 46726 (0,3)2135'96 1 46802.4 (2,412134.62 00 46832.0 (i.3'2133-67 5 46852.7 46846 (0,2)2129.46 2 46945.:! 46930 (i.-'il,(o,i)2128.22 3 46972.72124,03' 2 47065.3 47058 (1,1)2120.00 1 47154.8 47136 <2,l)2118.51 0 47188,0 (1,0;2114.82 OJ 47270.2 47262 (2,0)The intensities of the bands present interesting peculiarities. P'ig. i shows the potential curves drawn to scale, for the upper and lower slates of this system and the transitions taking place according to Frank-Condon princi­ple. The parabola of intensities thus obtained is indicated by a continuous line on the right side of the figure, inset in the small table giving tlie observed intensity distribution among the bands. It is a very wide and open one with the vertex shifted towards higher v "  values, the (o, 3) and (o, 4) bands being the most intense of the entire systems.Another feature of this system is the existence of only three v" progressions after which there is an abrupt teriuinatiuu of the bands ; there is no band with v ’> 2 .  This is considered to be an instance of predissociation, not found in any of the other systems of H gl so far analysed. The phenomenon of predis- socialion first observed in the S3 bands has since been noted in band systems of 3cvei;al other molecules (cf. Jevons 'Report' 19ja). In S3, two points of predis- sociatiou were observed and abrupt changes in the appearance of the bands occur at these points ; further, the bauds which have diffuse structure inUltraoiokt Band SyslemB of ,ho Marcury Iodide Maleculc 151HSy,U„e^pooiF i g .; * *v>-• t• (WF i g . s152 C. Ramasastry and K. R. Raoabsorption do not at all occur in emission. Similarly in the IS system of nit­ric oxide, bands with v ' > 4  are observable in absorption but not in emission. In yet other bands, such as the v" progression of the N2 second positive system a sudden cut oflF occurs in emission and the systems do not occur even in absor­ption. All these characteristics have been interpreted as due to the interaction of the upper state with an unstable electronic state of the molecule giving rise to radiationless transitions. The repulsive curve of such a possible electronic state, inter.secting the curve for the upper state of the H-system is indicated in Fig. 2 which shows the potential energy curves for the O and H-systems of the H gl molecule.’ A complete understanding of the nature of the predis­sociation is not yet possible unless the absorption of H gl in this region is also studied in detail. Experiments with a view to studying this particular feature are in progress and further di.scussion will be presented later. 1The vibrational constants, the estimated value of the dissociation mergy and K(atom) for the upper and lower states are given in Table V I. The values indicate a common lower state, same as that for the C and D systems. '.^ The nature of the upper electronic state is difficult to determine. Some of the bands of the G-system arc accompanied by fainter sub-bands which cannot be of isotopic origin. They are probably P components if the upper electronic state of this system is a V . For the H-systera, the upper state is probably a=S.T able V I7t'o' 7Vo " D' j D'' Ktitf^ m Dissociation products of the upper state,G 88.4 1257 1.21 0.4.4 6.48 Hg(ip) +I(2p)II 97.1 125-3 0^6 0.44 5.63 IIg(5P)-t-I(*P)Physics Dbpaktmknt Andhra llNivitRsirY WaiTaiu.R E F E R E N C E SCnrti.s and Evan.« (1933) P r o c .  R o y .  S o c .  A HI, 603.Howell ti9/13) P r o c .  R o y .  .^oc.  A 182, 95.Jevons (1932) Report on Rand Spectra, Page 201. Prilheshejewn (1932) P h y .  Z .  . S o w f e t .  1 1S9.Rao, vSastry and Krishnaiuurty (1944) h i d  J o u r .  P h y s ,  18, 323 Rao snd Rainachandra Rao {1944) C u r r e n t  . S c i e n c e ,  13, 279 Baiiikrishna Rao and Rao (1946) I n d .  J o u r .  P l i y . t .  20, 148, VenkQle.s\varln (1946) ^nd. A c a d .  ^Ici. 21 A, 473. Venkateswarlu (1946) I b i d .  21A, 480.Warren (193s) Pby- Rev. 47, 1,

Ultraviolet Band Systems of the Mercury Iodide Molecule. Part III

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/1396/1/Ultraviolet%20band%20systems%20of%20the%20mercury%20iodide%20Part%20III_C%20Ramasastry.pdf

Ultraviolet Band Systems of the Mercury Iodide Molecule. Part III

Abstract

Similar works

Full text

Available Versions

IACS Institutional Repository