Ramanadham, R

Ramasastry, C

Rao, G C S Ramachandra

English

IACS Institutional Repository

16 EMISSION BANDS OF THE PO MOLECULE"" By R. RAMANADHAM, G. V. S. RAMACHANDRA RAO AND C. RAMASASTRY ". (Rcccit'cd for PUbli+ttOI1, October 12, 1946) (Plate VIII) .\. ABSTRACT. In the course of an invcst~ation on the bauds of the I'~ molecule, exdfed under different conditions, the cbaraderistie.:ballds, ascribed by previous investigators to the PO molecule, in the region.\ 2600 and.\ .~3i)(I~.:nre found to bt: strongly el11iltedjin a wide open heavy Cllrrent arc between graphite polesi.containing phosphorus pentoxide. The bands at .\ 3300, which are not yet analysed, are parily red and violet degraded. Several attempts to include all the heads into one systel11 h~ing failed, the I ed-degraded bauds are analysed into one vibrational system and the violet-degraded bands into another sys'em, suggested tt) be due respectively tt) the electronic transitions 2l-2n and 2n -.. 2n with a common lower 'n state, same as the ground 'n ~tat(~ of .\ 2600 system, established by Ghosh amI Ball and by Sen Gupta. INTRODUCTION Band spectra of the diatomic oxide molecules of Group V-h c1emcnts havc bcen extensively studied alHI our knowledge of these has hCen11l11Ch extended in recent yeats (Collllelly, 1934; Sell Gupta, 19.39, 1944, 1945). Four systems ('Y, f3, Sand 6) arc analysed in NO, one in PO, two systellls (A and B) in AsO, threc (A, B and C) in ShO, and one in BiO 1110leclIle. In all these homologous molecules it has been suggested that the lower ground state is a 'II and the upper is either a 2~ or a 2H, giving rise to doublet systems of hands with the 'II interval, increasing frolll I'll cm-1 for NO to 2272 cm-1 for SbO. Although the main fcatmcs of these spectra arc known, it is ohvious that for a complete correlation there is need for further inVestigation, particularly of the bands of the oxides oi phosphorus and of hismuth. 'fhe carly work 011 the PO bauds was ~lll\llllarisell hy Pctrikalll (1928) who investigated these bands in emission amI in ahsorption and reported the existence of two characteristic :lystems for this lllolectllc, one at }.. 2600 aud another in the regioll }.. 3300. Ghosh and Ball (1931), however, were the first to report a complete vibrational analysis of the more refrangible of thesc two systems. It was shown to l~ollsist of double douhle-hl·adcd hands analogous to the 'Y bands of nitric oxide, with wcll·marked seqlH:l1(,CS and represented by the vihrationai cOllstallts, V, =40 264.7 cm- 1 40488.5 crn- I (,/=1391.0 10"=1230 .6 " x'w'=7·6S x"wll =6.52 The rotational structure was investigated by Sen Gupta (1935) who c!>tablish· eel tllEl electronic tral1sition of th is syslem as 2l: - 211, with the 211 interval * Communicated b~· Prof. K. R. RII(I 162 R. Ramanadham, G. V. S. R. Rao and C. Ramasastry equal to 224 cm- I . But the less refrangible system at A 3300 remained as yet unanulysed. Curry, Herzherg and Herzberg (1933) recorded the following 1Ilolecular constun ts, bJo'= 11SI, WO"=I228, but no detailed analysis has, as far as the authors arc a ware, been published till now. Even the published \\"ave-length data of the bands does not appear to be definite; the measurements made by Petrikaln do not cOirespond wel.! with those hy Genter. In view of this and the peculiar appearance of the bands a study of thIS system was l1uderlaken. E X P It RIM E N T A I, The experimental work on the bands formed part of an earlier iuvestiga-tion on the P2 bands (N. Rao, 1943) in the course of which several different sources of exciting the bands were ut.ilised. The PO bands were found to be strollgly emitted in a wide-open heavy current arc between carbon electrodes fed by phosphorus pentoxide and absent altogether in the ordinary trans-former discharge through PlJ5 , which only gave bands due to oxygen, phosphorus und CO or NO. The arc consisted of a lower {Jo!'.itive graphite electrode about l.S em. in diameter in which a cylindricai hole 10 mm. x 7 111111. was drilled, and the phospholUs pemoxide powder tlUnsfcrrecl directly into it. The upper graphite electrode was about 6 111111. in diameter. The arc fed by a cutrent of 7 to 8 amperes was drawn out into a long flame, the central portion of which was focllssed 011 the slit of the spectrograph. Preli-minary photographs before introducing P205, taken with the graphite rods alone under identical conditions, served as comparision spectra. A well-developed band system was obtaim'd in the region fr011l A 3S80 to ,\ 31S0, the 11I0st peculiar feature of which is that sOl11e of the bands were degraded to the red aud others to the violet. This feature was recorded also by Pctrikaln who photog-ruphed the bands in absorption using specially prepared phosphorus trioxide. Plate VIII is a reproduction of the spectra obtained with a Hilger quartz Littrow spectrograph type E 1, with and without phosphorus pentoxide in the electrodes aud iroll arc comparison. The exposure was for about half-an-hour. The wavelengths of all the band heads in order are recorded in Table I; they closely agree with the published measurements due to Geuter. The letter V or R in the last colullIn indicates the direction of degradation (violet or red) of the band. ANALYSIS As mentioned earlier, each of the diatomic oxide molecules, homologous with PO, gives band systems due to transitions into a 'II state from one or more upper states which may be eitber a 2l; or a 'IT. The PO bands under Emission Bands af PO Molecule 163 'fABLE I Bands o( PO lllolet'ulc '. Wave length ,r; , Cla~si6(~atiou Intensity wat. nUluber -Violet~<le~~~d;d /. --R~;I.c1cg;"\lk;1 : "~ system system ---- ._-----. __ ._--_.+------_._-_ ...... _----- -----------------_. 3579·4 3578.6 35679 35632 35626 3550 .2 35426 3541.9 3539 0 3530 . 1 3521.2 3478.6 34708 34601 345(19 3442·4 3431.7 3424·4 341 3.9 34°9·7 340$7 3397J; 3396 4 3387.8 3386.3 3379.8 3366.1 3362.5 3360.8 3.~46·3 3340 7 3339·7 3328.4 3321.0 3319.8 3312.0 3303.2 3301.1 3296.5 3286.0 3280.4 3270 .4 3269.3 3266.8 3255.2 3253.6 3246.2 3238-6 3217.4 3204·3 3J98.9 3198.2 3188.2 3J 8o·7 3173.4 3164·9 3149.8 1 o o 1 2 I I ~ 3 3 3 3 2 3 2 3 3 2 2 3 2 2 3 3 2 3 :I :I 3 3 I 2 2 I :a 2 :I 1 I I 2 2 2 t 2 ) '~i93(> :fa 7936 ,128019 :.80.';7 )8061 !p81 S9 1118220 ~H22S !~8249 R83 20 28391 28739 2880 4 288t;3 2896<} 29::>41 29132 29194 29284 29320 29354 29422 29435 29509 29522 29579 19647 29731 29746 2987$ 29925 29934 300,;6 30103 30Il4 30185 30265 30284 30327 30423 30 475 30569 30579 306"2 307II 30 726 30796 30869 31027 3 II 99 3J252 312';9 31357 31431 31503 31587 31739 V (3.5) V V (2.4) V V V (0.2) V V V (2.4) V (I. 3) V 10. 2) V (2, 3) V (I. 2) V 13. 41 V (0. 1) V (2, 3) V V II, 2) V V (0,1) V (0. 0) V (2,2) V (I, I) V (0,0) R R (3.4) R (I, 2) ... R (0. II R R (I. 2 I? R H (4, 4) R (4,4) R (2,:.1) It (3, 3) H (3 •. ~1 H (I, II R (2,2) R (2, 2) R (0,0) R (I, II Rh, II R(IO, 81 R (0,0) R IS, 4) n (10,8) R (3. 2) R (2, II n (7,5/ RI1,0) R 16,4) R (7,5) .R (I, 0) R (6.4) R (9,6/ 164 R. Ramanadham. G. V. S. R. Rao and C. Ramasastry investigation may be expected to be due to a similar electronic transition. If they all belong to one system, say 2l: - 2IT, they must consist of double double-headed bands with the doublet width equal to 224 ems-I. Examination of the bands has, no doubt, revealed several heads with the wave-number intervals either equal to or not far from the value of 224 ems·- J • But not all the component heads show the doublet structure: some of these are close dottblets and others are not. This has led to the suspicion that the bands under investigation may comprise of two overlapping systems. Allother peculiar feature leading to the same view is that sOllie of the bands are red-degraded (mostly those which show close doublet structure) and others are violet-degraded, although instances arc known of b:lDd systems where, in one and the same system, there is a change in the direction of degradation of the bands. The previous investigators, e.g. Petrikaln, as al~o Curry, Herzberg and Herzberg seem to have attempted the analysis of {he PO bands on the supposition that there is only one system and the latter authors have suggested a possible 2II -'n transition. 'I'he first attempts of the authors were to examine the possibility of illc1uding all the band heads into one and the same system either a 2~_2n or a ~1I-2II (the latter transition possibly giving rise to single-beaded bands). The constants recorded by Curry, Herzberg and Herzberg were also considered and on the basis of these values the possibility of fitting all the bands into one system was studi~d. All these attempts having failed, recourse was taken to the alternative possibility of regarding the bands as belonging to two overlapping systems. The analysis thus arrived at is shown in Tables II and III. TABLE II Vibrational Analysis of the PO Bands. (Red-degraded system.) (System A.) 0 2 3 4 5 o Q 30423(3) Q 30185(3) 28969(1) R 30384(2) Q 31503 (2) 30265(3) Q 31252(1) 30036(3) R 30II4(1) Q 30103 (3) Q 31072(11 2gB75(3) 2 R 29934(2) g 29925(2) 28804(1) 30869(1) 3 R 29746(2) 8 29731 (2) 30726(2) 4 Q 30475(1) Q 5 Q 31587 (I) Q 31557lp) , 6 8 I 31431 (li) 3[199(d • • .. 1 RAMA.?\'ADHAN, RAO AND RAMASASTRY FLA'l L \ ill (a) Iron Arc (b) p"O:; in Carbon Arc showing PO bands (C) Carbon Arc (a) (b) (c) I ! I i 3400 3300 32CO 3100 PO Bands Emission Bands 0/ PO Molecule TABLE III 165 Vibrational Analysis of the PU Bands. (Violet-degraded system.) (Systcm B.) o 2 2 o 30,56c}(2) 3°796(3) 29354( 3) 29579(.3 1 ~159'O) '39x(1) J284(3) ~509(3) 29 1<)4(3) 29422(3) a801,)h) 28249(1) 27930(1) All the red-degraded bands form one system. The Q head interval is nearly 224 cms- l and in most cases the component R beads are also detected. The electronic transition is probably 2~ - 2II. The bands are approximately represe11ted by the formula \/= 30260.8 + [Io94(V' + ~) - 14.5('V" + W] - [I234(v" +~) -9.5( 'V" + ~)'] The violet-dcgraded bands are all arranged into a second system. 'J'he bands are single-headed. They are perhaps due to the transition 2II - 2II and may be represented approximately by the formula v= 30606.5 + [II5I.9(v' + t) - 14.2( 'V' + ~)2) - [I224.('V" + i) - 6.5(v" + .)1) 402.65 30606 30261 2 'TT('!"" •• ~/' 2:E 'J IQ '( ~ ~ f -~ ~ ... III rl.c.,rof)/c fr4nsiNcn. In Po 6."dfl. Flo. 1, 166 R. Ramanadham, G. V. S. R. Rao and C. Ramasastry If tbe analysis proves correct, an interesting feature of this system, which deserves mcntion, is that while the bands thcmselves are degraded to the violet, the sequence degradation is towards the red. 'the lower state for these two band systems is considered to be identical with the lower statc of the most refrangible systcm which was analysed by Ghosh and Ball. 1'hcre are thus three identified systems among the PO bands which may be designated as A, H, and C, in the order of diminishing wavelength and the electronic transitions conccrned, may be represented diagramatically as in the Fig. 1. PHYSICS DJiI'ARTIIIIlNT, ANllHKA UNIVllllSITY, WAl,rAllI REFi~RENCHS C.onnelly, 1934, Proc. Pity. Soc. (I.ond.).16, 790. Curry, Herzberg and Herzberg, 1933. Zeits. f. I'lIys., 86. 364. Ghosh and Hall, 1931, Zeits. /. /111)'5., 71, 36~. Pearse and Gaydon, It Identification of Mulecular Spectra," p. 162. Petrikaln, 1928, Zefts./. l'hys., B1, 395. Rao, Nsrahari. 1943, Ind. JOllr. l'llys .• 17, 135 and 149· Sen Gupta, 1935,·Proc. Phy. Soc. (Lond.l, 17,247. Sen Gupta, Ind. JouT·Phys., 1939, 13, 145; 1944. 17, :116; 1945,18,183. 

Emission Bands of the PO Molecule

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Emission Bands of the PO Molecule

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