This paper deals with the raman spectra of different modifications of crystals.@IAC

Gupta, J

Sirkar, SC

IACS Institutional Repository

ON THE RAMAN SPECTRA OF DIFFERENT MODlFlCATlQNS OF A FEW CRYSTALS. AND J. CUPTA IRcrefwd for pwbrtcufron, Octobw 16, 1936.) kMTRhCT.-The Rernan spRtra d diflwmt modifimti~na of crpstnla of p d i c h b  kntrnt, P . d i b m i o b w r  and salgl~nr hmc been studied at different t e m p a h v m  including tbat oi liquid sir. It has h observed that in the cam of the last two of the above subtancts w abrupt changr takes place with the transformation from one modificatior~ to the 0th- in tbe witinns of the new lincs which appear in the cane of the miid skate in the neinhbolrr bood of the laylcigh line. In the mw of p-dichlorohuent, however, not only mnt  of thcat wtv lines but aho son* Raman lines due to inttrmolmlar vibrmtim of the aiugle l~~okcnlt e n  sbiftcd on cwling the crystals once in ice, end it ia not dthitely known whether tbt httin is rhanged with this emling. On l o w c t h ~  the ttmpcrntluc of the crpstals of tht hrv suhstaacfs to that of liquid air, the new iinca shifted sway from the Reyleigh Hat, bat the lincer cocmcieat d ~xpaashl  celmtntcd from the magnitude of ther shim with the help d tht tbcory of lattice oscillation stemsto bt too high. The n h  -Its prt b s a c d  md it 46 mggcsted that the lines in qamtion may have their mi& fn P i h t h  of flymerid mps. It was shown by 8ech and Ebbinghaus' that an abrupt eontrPetron d volume bkcs place when crystals of $-dichlorobwzene, +dibromokmne, P-toluidine, sulphur and a few other organic substances arc mld below a -in mitical temperature which is different for the different s u b ~ c c s .  From this observation they concluded that there are two nldlifications of the ctystals d a h  of these aubetsnees. The rnodilicatims below and above the trendmatiam point are called m. and /3.mdifications rapectively. Vuks' has recently studid the Raman spectra of the two mdificgtims of crystals of #-dichlmhwenc and baa observed that of the m w  Raman lines which appear in the neighbmlt- hood of the Rayleigh line in the -rum of l i h t  smttcml by thc sahtunc* in the solid OW, me d~ifted slightly wit11 thr tratisfwmetinn tmrl me mndificatial to ~e &. From Uiia fact he hna concludfd thnt these linm h ~ w  their uri#rin 

ON THE RAMAN SPECTRA OF DIFFERENT MODlFlCATlONS OF A FEW CRYSTALS

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