• N Rajeswara Rao

      Articles written in Pramana – Journal of Physics

    • Infrared intensity analysis of some MXY2 type molecules

      Pratibha Naik N Rajeswara Rao

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      Infrared intensity analysis of MXY2 type molecules has been attempted. The dipole momentμ of C=O is obtained to be different for different moleculesviz. for CH2O, 1.9052; for COCl2, 1.1517; for COF2, 0.6340; and for COBr2, 0.7687. Similarly in the case of CSF2 and CSCl2μC=S it was found to be 0.2473 and 0.2983 respectively. This shows that the effect of the electro-negative halogen atoms is very important.

    • Infrared intensity analysis of CH2Cl2 and CD2Cl2 in vapour and liquid states

      Pratibha Naik N Rajeswara Rao

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      In the infrared spectra of molecules with more than one C-H bond the symmetric and antisymmetric stretching bonds often overlap, causing uncertainty in the intensity analysis. For CH2Cl2 and CD2Cl2 in the vapour state, the two bands overlap to such an extent that Straley who takes it as one band attributes it to antisymmetric stretching while Saekiet al assign it to the symmetric stretching. Following the method of analysis initiated in this laboratory, we have solved this problem by ultimately obtaining intensities separately forA1 andB2 species. The band is mostly due to the symmetric stretching, 0.06 out of the total of 0.31 contributing toB2. Thus, this gives a method of separating the intensities of bands which are highly overlapping.

    • Infrared intensity analysis of molecules C2H6, C2D6, C2F6 and CF4 zero and first order approximations

      V Buddha Addepalli N Rajeswara Rao

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      Infrared intensity formulae for C2H6 and C2D6 are derived following the first order approximations. Using the experimental intensities in the intensity equations, the first order coefficients are calculated. They are observed to be negligible compared to the accuracy limits within which the intensities can be measured. Correlating the experimental intensities to the intensity expressions of C2F6 and following the zero-order approximations, the bond dipole moment μ and its derivative e are calculated for the C–F bond. Substituting these in the intensity equations of CF4, transferability of the bond moment parameters is discussed.

    • Evaluation of photoelastic constants from first-order Raman intensities of MgF2

      G Swarna Kumari N Satyavathi N Rajeswara Rao

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      A formalism to connect first-order Raman intensities of MgF2 and its photoelastic constants is developed by developing a method of writing internal coordinates in terms of displacement gradientsuij which are not symmetric. It is found that for crystals containing only one line inA1 species, the ratiosP13/P33 and (P11 +P12)/P31 can be directly evaluated from the intensities, without having to derive the intensity formulae; while (P11 +P12)/P13 is independent of the intensities as well as the refractive index of the crystal. It is a function of only the dimensional parameters. In this crystal, since the speciesB1g andB2g also contain only one line each, the ratio (P11P12)/P66 can also be directly obtained from the intensities.

    • Infrared intensity analysis of CHCl3 and CDCl3

      L D Wahegoankar N Rajeswara Rao

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      IR intensity formulae can be derived in the formI=L′ A; I being square root of intensityI2, has sign ambiguity. Equations likeI′ I=A′ LL′ A=A′ GA have been used to solve the sign ambiguity. There is only one equation for each species. This position has now been improved by introducing a new concept about this sign ambiguity and solved for electro-optical parameters taking a pair of molecules CHCl3 and CDCl3 for demonstration. This incidentally solves the sign ambiguity problem of polar tensors which are calculated for these molecules.

    • Force constants from intensity analysis of molecules CH3Cl and CD3Cl

      V Dayanand K Ravindranath N Rajeswara Rao

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      The secular equation (GF - Eλ)L = 0 contains more force constants than can be calculated from the equations formulated using the frequencies. For a 3 × 3 matrix, there are 6 force constants but only 3 frequencies. Attempts were made by others to estimate all the 6 constants to satisfy the frequencies and Coriolis constants and rotation distortion constants. However, many attempts are not made in these estimations to satisfy the intensities. A full complement of equations is derived to evaluate all the force constants combining the intensity equationsI =L’A withLL’ =G and evaluated the force constants ofA1 species of CH3Cl and CD3Cl. A simple analysis of a 2 × 2 matrix shows thatF12/F22=G12−1/G22−1 as reported earlier.

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