• C S Venkateswaran

      Articles written in Proceedings – Section A

    • Raman spectrum of sulphur in the solid and liquid states

      C S Venkateswaran

      More Details Fulltext PDF
    • The raman spectra of some metallic halides

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The paper describes the results of the study of the Raman spectra of the halides of cadmium and zinc as well as of magnesium chloride, magnesium bromide and aluminium chloride. All the halides of cadmium and the chloride and bromide of zinc have yielded lines wich show the existence of homopolar binding in them. The spectra of zinc chloride and cadmium iodide were fairly intense in contrast to the weak and doubtful lines obtained by the previous investigators, and indicate a linear triatomic model for them analogous to those of mercuric halides.

      Marked differences in intensity, sharpness and frequency have been observed in zinc chloride, cadmium bromide and cadmium iodide from crystal to solution and with different solvents. The presence of halogenions in solution also affect the characteristics of the spectra considerably. These are explained partly by the change in the degree of ionisation in different solvents and partly by the influence of the solvent molecule on the fundamental oscillation frequencies of these compounds. It has been pointed out that the Raman effect data obtained for the cadmium halides do not furnish sufficient evidence for the formation of complex ions of the type CdX4″ in solution.

      Magnesium chloride, magnesium bromide and aluminium chloride gave on Raman lines. A pronounced effect on the bands of water was noticed in each case.

    • The raman spectra of iodic acid and the alkaline iodates as solids and solutions

      C S Venkateswaran

      More Details Fulltext PDF
    • The raman spectrum of phosphorus

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectrum of yellow phosphorus as vapour, liquid, solid, and solution in carbon disulphide has been obtained. Only small changes in frequency are observed while passing from solid to liquid and to vapour, indicating the non-polar character of the molecule. The spectrum of carbon disulphide is rendered weak although the spectrum of phosphorus in solution comes out strongly. A strong fluorescent band extending from 6230 Å. U. to 6550 Å.U. has also been recorded in all cases.

    • The raman spectra of dioxane and tetralin

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectra of dioxane and tetralin have been obtained using the filter technique. The spectrum of dioxane consists of twenty-four lines of which fourteen are reported for the first time and resembles closely that of cyclohexane. Tetralin has also given eleven new lines. The results obtained are discussed with reference to the structure of the molecules.

    • The fluorescence of ruby, sapphire and emerald

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The photo-luminescence of natural crystals of ruby, sapphire and emerald (beryl) has been studied at room temperature with a Fuess spectrograph of high light-gathering power. The ruby has yielded a number of new bands which have not been obtained hitherto. The spectrum of sapphire corresponds closely to that of ruby but with slight differences. The spectrum of emerald consists of two sharp lines at 6806 and 6835 accompanied by other diffuse bands and is compared with that of ruby. The fluorescence in sapphire and emerald is also discussed with respect to the origin of luminescence in them. Photographs of the spectra illustrate the paper.

    • The Raman spectra of some formates and the constitution of formic acid

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectra of the formates of sodium, calcium, cadmium and lead have been investigated both as solid and as aqueous solutions and the following average frequencies have been obtained for the formate ion :-2834, 2734, 1717, 1534, 1347 and 857 cm.-1 The presence of the lines at 2834 and 2732 gives direct experimental evidence of the existence of CH group in formic acid. The solids have yielded faint lines also at 2976 and 1398. The frequencies are compared with those of formic acid and its esters and acetic acid and acetates. The presence of the line at 1534 seems to be characteristic of the formates.

    • The Raman spectra of ortho-phosphoric acid and some phosphates

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectra of ortho-phosphoric acid for a wide range of concentrations and of the primary, secondary and tertiary phosphates of sodium, potassium and ammonium have been obtained. The acid has yielded new lines which indicate the ionisation of H3PO4→H°+H2PO4′ and the further ionisation of H2PO4→H°+HPO4″. Weak lines characteristic of the OH oscillations have also been observed for the acid. The three series of phosphates give characteristic spectra which are identified as due to H2PO4′,HPO4″ and PO4‴ ions. The frequency shifts of the PO4 radical are compared with those of SO4 and SeO4 and the force constants are evaluated.

    • The Raman spectrum and electrolytic dissociation of selenic acid

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectrum of selenic acid has been investigated in the state of solid, liquid and aqueous solutions of concentrations varying from 92·5% to 7 ·5% by weight. The solid has yielded eight lines with frequency values of 1383, 930, 896, 778, 766, 374, 355 and 327. Marked changes in position, intensity and character of these lines are observed during the transition from the solid to the liquid and then to the aqueous solutions. The gradual disappearance of some of the lines and the increase in the intensity of some others and the appearance of new lines are explained on the basis of the stepwise dissociation of the acid, namely, H2SeO4 → HSeO4′ + H° and HSeO4′ → SeO4″ + H°. The results indicate that the first stage of ionisation starts from the solid and the second stage from about 50% concentration. The results are compared with those of its analogue, sulphuric acid and conclusions are drawn regarding the structure and the apparent shifts of the bands in both these acids. The changes that take place in the lines during the transition from the solid to the liquid are characteristic of the hetro-polar nature of the chemical bond in the acid molecules.

    • The raman spectrum and electrolytic dissociation of selenic acid

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectrum of selenic acid has been investigated in the state of solid, liquid and aqueous solutions of concentrations varying from 92·5% to 7·5% by weight. The solid has yielded eight lines with frequency values of 1383, 930, 896, 778, 766, 374, 355 and 327. Marked changes in position, intensity and character of these lines are observed during the transition from the solid to the liquid and then to the aqueous solutions. The gradual disappearance of some of the lines and the increase in the intensity of some others and the appearance of new lines are explained on the basis of the stepwise dissociation of the acid, namely, H2SeO4→HSeO4′+Ho and HSeO4′→SeO4″+Ho. The results indicate that the first stage of ionisation starts from the solid and the second stage from about 50% concentration. The results are compared with those of its analogue, sulphuric acid and conclusions are drawn regarding the structure and the apparent shifts of the bands in both these acids. The changes that take place in the lines during the transition from the solid to the liquid are characteristic of the hetro-polar nature of the chemical bond in the acid molecules.

    • The Raman spectra of selenious acid and its sodium salts

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectra of selenious acid as crystals and as aqueous and alcoholic solutions of varying concentrations as well as those sodium biselenite and sodium selenite are investigated. The solid has yielded a spectrum rich in sharp and intense lines, of the following frequencies :—124, 199, 254, 287, 299, 364, 524, 597, 706, 862, 889, 909 and 940 cm.-1 The lines broaden out and undergo variations both in frequency shift and intensity.

      The changes in relative intensities of the two lines, 706 and 597, are particularly remarkable and are explained by postulating two types of molecules namely the symmetrical form and the unsymmetrical form in dynamic equilibrium in the acid. In the solid and in the solution in methyl alcohol the latter is the more predominent type and in the aqueous solution almost the whole of the acid is converted to the former type. Thus the Raman effect data are made use of for the first time to explain the pseudo or the true nature of the acid.

      The spectra of aqueous solutions of different concentrations indicate that the dissociation of the acid is weak and that, the proportion of molecules dissociated to HSeO3′ ions remains practically constant throughout. The line 895 is assigned to the HSeO3′ ions. The results are compared to those of its analogue, sulphurous acid. The other lines in the spectrum are attributed to vibrations of definite molecular species by comparing them to the lines in the sodium salts of the acid.

      Three low frequencies of the solid at 124, 199 and 256 are discussed in the light of the existing theories and their probable assignment is indicated.

      The influence of change of state of the Raman spectra of the acid is briefly discussed. The broadening of the lines in the liquid is explained as due partly to association in the molecules and partly to the composite nature of the bands.

    • Polarisation of Raman lines in some inorganic acids

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The polarisation of Raman lines of nitric, iodic, sulphuric, selenic and selenious acids is investigated making use of the usual double-image prism method. All the lines of the concentrated nitric acid except one at 1538 which is attributed to the deformation oscillation of the hydroxyl group, show varying degrees of depolarisation which are less than the limiting value 6/7. The lines due to the nitrate ion possess a state of polarisation which is in agreement with the plane equilateral structure attributed to it. From the results of polarisation six lines belonging to the undissociated nitric acid molecule are identified with the known modes of oscillation of an unsymmetrical pyramidal model having a structure. The state of polarisation of the Raman lines of the H2SO4 molecule and its dissociation products, HSO4′ and SO4″ ions generally supports the assumption that all the three forms are tetrahedral and that HSO4′ ion is the most distorted of the three. Structural formulæ of the three species and the mechanism of dissociation from one form to the other are discussed in relation to the degree of depolarisation of the breathing frequency. Polarisation of the Raman lines of selenic acid is analogous to those of sulphuric acid. The results of polarisation of the bands of iodic acid as well as selenious acid generally support the previous assignments of these bands to different molecular species.

    • The raman spectra of sulphur and phosphorus - Part I. Polarisation and molecular structure

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The polarisation of Raman lines of sulphur and phosphorus is investigated with reference to their molecular structures. An intense Raman spectrum of liquid phosphorus has yielded three lines the state of polarisation of which conforms to the Raman-active vibrations of a tetrahedral molecule. The molecule of sulphur is considered to be a symmetrical puckered ring made up of two squares of four atoms each, one square placed at 45° with respect to the other. To explain the strong infra-red absorptions, the neighbouring atoms in the plane of each square are assumed to be connected with co-ordination bonds which give rise to electric dipoles causing absorption. The two lines 470 and 216 which are well-polarised are assigned to two symmetrical oscillations of such a model, 470 to the vibration in which the four atoms in each square move towards or away from the centre of the square and 216 to the vibration in which the two squares move towards or away from each other. The lines at 150 and 434 are completely depolarised and belong to anti-symmetric vibrations. The well-known changes of sulphur on heating are explained on the basis of this new molecular structure. A method of distilling high-boiling-point substances is also described in the paper.

    • The Raman spectra of sulphur and phosphorus - Part II. Lattice oscillations

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The existing theories regarding the origin of the discrete Raman lines in the solids in the place of the wings accompanying the Rayleigh line in liquids are reviewed. An intense sharp line at 36 cm.−1 has been reported for solid phosphorus which broadens to a depolarised wing in the liquid state. This frequency agrees well with the frequency of vibration of the crystal lattice calculated from the melting point of phosphorus and therefore, owes its origin to the latter. The Raman line at 88 cm.−1 observed for rhombic sulphur appears as a weak diffuse depolarised line in liquid sulphur at 80 cm.−1 and is also attributed to lattice vibrations. The objections for assigning these lines either to Pauling rotation or to intermolecular oscillations of polymerised groups are indicated.

    • The hydroxyl frequency in the Raman spectra of acids and acid salts

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectra of sulphuric, iodic, selenious and telluric acids and sodium dihydrogen phosphate and potassium bisulphate have been obtained under long exposure and using complementary filters. In every case, a band characteristic of the O−H group has been recorded. The band is weak and diffuse and is shifted to a frequency considerably lower than that due to free hydroxyl group. The results are discussed in relation to electrolytic dissociation and molecular structure of these compounds. From the nature of the spectra, the characteristic features of the Raman band due to the so-called hydrogen bond are deduced. Some new Raman frequencies in selenious and telluric acids are indicated in the paper.

    • The raman spectra of some inorganic compounds

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectra of telluric acid, and the chromate, molybdate, tungstate, periodate, bisulphate, chlorate, bromate, and azide ions are obtained. From these spectra, Te (OH)6 is shown to be octahedral, CrO4″, MoO4″, WO4″ and IO4′ ions as tetrahedral, ClO3′ and BrO3′ ions as pyramidal and N3 as linear and unsymmetrical, in structure. The splitting of the frequencies due to the removal of degeneracy by distortion of ions in the crystals, are observed in a few cases.

    • Low frequency Raman lines in organic crystals

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The Raman spectra of the low frequency region between 20 and 130 cm.−1 have been recorded for fourteen organic solids and the influence of rise of temperature upto the melting point on these lines in a few cases has been investigated. These lines in the solids are interpreted as arising partly from translational and partly from rotational oscillations of the molecules with definite phase-relationship with each other in the lattice. Liquid salol exhibits a fairly intense wing near the Rayleigh line which does not appear in salol glass at liquid air temperature. This observation and other experimental facts such as extension of the wing, the distribution of intensity and the influence of temperature on it and the degree of depolarisation at different points in the wing and the corresponding lines in the solid do not support the hypothesis of Gross and Vuks that most of the wing in liquids arises from the lattice Raman lines and that the liquid state is quasi-crystalline in structure. A band observed in liquids, benzophenone, diphenyl ether and diphenyl in the place of a line above 100 cm.−1 in the solids is attributed to a deformational oscillation in the molecule itself, which seems to be characteristic of bicyclic compounds.

    • The Raman X-ray reflections in organic crystals: I. Naphthalene

      C S Venkateswaran

      More Details Fulltext PDF
    • The Raman X-ray reflections in organic crystals: II. Benzophenone

      C S Venkateswaran

      More Details Fulltext PDF
    • The Raman X-ray reflections in organic crystals: III. Hexamethyl-tetramine

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The X-ray reflections from the (110), (200), (211) and (111) planes of hexamethyl-tetramine shows that the intensities of the dynamic reflections follow the same order as the intensities of the corresponding static reflections. The Raman spots of the crystal are relatively sharp compared to those from organic and inorganic crystals of complicated structure. These observations are readily explained by the fact that the molecular and the crystal structures of the substance have a high order of symmetry and that for the principal planes there is only one Raman X-ray active lattice vibration which corresponds to a movement of the two molecules against each other along the cube diagonal. The geometry and orientation of the spots are also found to depend on the direction of the phase-waves connected with the above vibration.

    • The lattice spectrum and the Raman X-ray reflections by rock-salt

      C S Venkateswaran

      More Details Fulltext PDF
    • The thermal energy of crystalline solids: Alkali halides

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The character table for rock-salt derived from the theory of groups applied to the unit cell containing four atoms of sodium and four atoms of chlorine, gives eight triply degenerate normal modes of vibrations. One of them corresponds to the translations of the cell as a whole, two are infra-red active and Raman inactive, and five are inactive both in the Raman and the infra-red. The overtones of the latter five modes should however, appear in the Raman effect. This analysis of the vibration spectrum of the rock-salt structure gives a complete explanation of the infra-red absorption spectra of the alkali halides observed by Barnes and the Raman spectrum of rock-salt obtained by Fermi and Rasetti. The two infra-red absorption maxima at 161 and 247 cm.−1 are taken as the two fundamental frequencies and the five frequencies at 228, 272, 298, 346 and 366 cm.−1 identified from the Raman spectrum reproduced by Fermi and Rasetti, are assumed to be the first overtones of the remaining five frequencies of the lattice. The latter also shows three broad bands with peak frequencies of 81, 42 and 20 cm.−1 These are shown to be the octaves of the superlattice frequencies of the second, third and fourth orders.

      A general expression is derived for the thermal energy of cubic crystals of the rock-salt type in terms of the lattice and superlattice frequencies. The expression is evaluated for rock-salt and sylvine for a wide range of temperatures which in the case of sylvine is 3° to 285° absolute. Two of the lattice frequencies for sylvine are given by the infra-red spectrum and the others are deduced from those of rock-salt. The calculated values in either case are in reasonable agreement with experimental data, showing that the thermal energy of crystalline solids is satisfactorily explained on the basis of the ideas indicated in the foregoing paper by Sir C. V. Raman and developed further in the present communication.

    • Interferometric studies of light scattering in gases

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      Light scattered backwards by four gases, namely, hydrogen, nitrogen, oxygen and carbon dioxide at high pressures has been analysed by a Fabry-Perot interferometer. None of the gases showed displaced components similar to those in liquids. For the heavier gases, N2, O2 and CO2, the Doppler broadening was observed to be too small to be detectable with mercury radiations. The pattern obtained for hydrogen showed a broadening and the half-breadth of the line was found to be of the order to be expected from Maxwell’s law of distribution of velocities. A weak background due to molecules having relatively high velocities was observed in the scattered patterns for all cases.

    • Interferometric studies of light scattering in mobile liquids

      C S Venkateswaran

      More Details Fulltext PDF
    • Interferometric studies of light scattering in viscous liquids and glasses

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      In an interferometric study of light scattering by highly viscous liquids, sharp and well-defined Brillouin components have been recorded for glycerine and castor oil. The intensity of these components in glycerine shows a progressive increase as the temperature is raised from 0° to 110° C, the central undisplaced component indicating a corresponding diminution in intensity. The Brillouin components appear with great intensity in cyclohexanol and glycol which are relatively less viscous. On the other hand, no displaced components are observed in glucose and in styrol and optical glasses. While the velocity of the thermal sound waves calculated from the Brillouin displacement agrees well with the supersonic velocity in cyclohexanol and glycol, it is considerably higher than the latter in glycerine and castor oil. The divergence between the ‘hypersonic’ and the ‘ultrasonic’ velocities diminishes as the temperature of glycerine is raised to 110° C. The appearance of well-defined Brillouin components in these highly viscous liquids indicates that the ordinary laws of hydrodynamics are not valid for the propagation of these high frequency waves in the medium. The results are also shown to be in contradiction to the predictions made by the theory of light scattering in liquids put forward by Leontowitsch. From the ultrasonic and hypersonic velocities in glycerine and castor oil, the bulk modulus,k, and the rigidity modulus,n, have been determined. The time of relaxation τ calculated using the Maxwell’s formula η =nτ where η is the viscosity, is in both cases greater than the time-period of the thermal sound waves, thereby furnishing an experimental proof of the thesis that the liquid behaves essentially as an amorphous solid at sufficiently high frequencies. These conclusions are also supported by observations on the dependence of the intensity of the rotational ‘wing’ on the viscosity of the liquid.

    • Interferometric studies of light scattering: Hypersonic velocities in liquids

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      The ‘hypersonic’ velocities for eighteen representative liquids are calculated from the Brillouin displacements in the light scattered by these liquids. The data are compared with those obtained by the ultrasonic method. No detectable dispersion of velocity has been observed in any liquid in going over from the frequency range of 10 MHz in the ultrasonic to 10000 MHz in the hypersonic region.

    • The raman spectra of organic compounds: Aniline

      C S Venkateswaran N S Pandya

      More Details Abstract Fulltext PDF

      An intense Raman spectrum of aniline has yielded thirty-nine lines. They are: 234 (4,.71), 280 (0, D), 330 (0, D), 387 (4, 63), 408(1), 532 (5,.62), 619 (5,.62), 700(1,), 757 (3,.71), 775(0), 810 (8,.28), 830 (8,.30), 888 (0, P), 938 (1,P), 987 (0 ), 996 (10,.26), 1029 (5,.28), 1060 (0, ), 1110 (0 ), 1149 (3, .78), 1168 (2, .55), 1200(0, P), 1230 (0, P), 1272(4,.33), 1340 (1, D), 1388 (1, D), 1456 (2,.62), 1499 (2, P), 1538 (2, P), 1590 (2, D), 1601 (10,.69), 1612 (2, P), 2922 (2, P), 3020 (0, D), 3046 (10,.53), 3066 (4, P), 3190 (1, D), 3362 (3, P), and 3423 (2, D). Thirty of these are assigned to the benzene ring by comparing these frequencies with those of benzene and its monosubstituted derivatives. 3362 (3 P), 3423 (3 D,) and 1538 (2 P) are assigned to the NH2 group and 830 (8, .30) and 408 (1) to the C–N linkage.

    • The raman spectra of organic compounds: Diethyl disulphide

      C S Venkateswaran N S Pandya

      More Details Abstract Fulltext PDF

      An intense Raman spectrum of diethyl disulphide and its polarisation characters are recorded. The spectrum consists of twenty-seven lines. Nine of these are observed for the first time. It is shown that nine of these lines (three of which are depolarised) belong to the ethyl group (C2 H5), and the remaining eighteen of which six are depolarised belong to the chain C2-S-S-C2. The results are discussed in relation to the problem of ‘free rotation’ about the S-S bond. It is concluded that six polarised lines are due to thetrans and twelve due to thecis forms; and that these two types of molecules co-exist in the liquid in equal proportions.

    • The raman spectra of organic compounds: Binary liquid mixtures

      C S Venkateswaran N S Pandya

      More Details Abstract Fulltext PDF

      The Raman spectra of two critical solution mixtures, namely cyclo-hexane-aniline and iso-butyric acid-water, are obtained and compared with the spectra of the component liquids. No changes are observed in the cyclohexane-aniline mixture. In the iso-butyric acid-water mixture the following changes are observed: Three fairly intense lines at 510, 1430 and 1654 cm.-1 of the acid disappear in the mixture and instead, broad lines appear at 519 and 1715. The strongest line of the acid at 800 cm.-1 becomes slightly broader and less intense. The strong water band at 3460 appears to be shifted to a slightly higher frequency. From a comparison of these changes with those reported for formic, acetic and trichloroacetic acids, it is concluded that at the critical temperature, the acid molecules change over from dimer to monomer state. This indicates that at or above the critical temperature, the two liquids in the mixture become homogeneous as in solutions. The results are discussed in relation to the cluster formation in the binary liquid mixtures.

    • The dynamic X-ray reflections in carbon silicide

      C S Venkateswaran

      More Details Abstract Fulltext PDF

      Raman’s theory of dynamical X-ray reflections and the thermal theory of diffuse X-ray scattering are critically reviewed. An investigation of the extra-spots in X-ray diffraction by the {2021} planes of a hexagonal type of carborundum crystal shows that the spots are sharp and their intensity is nearly independent of temperature for a wide range from −180°C. to 600°C. and for different orientations of the crystal. It has been shown that they can be explained as due to the coherent modified reflections of X-rays by the eigen-vibrations of the crystal lattice having a frequency of 830 cm.−1 which is observed in the infra-red absorption as well and that the diffuse thermal scattering due to the long eleastic waves is not responsible for their appearance.

  •  

© 2021-2022 Indian Academy of Sciences, Bengaluru.