• Chintamani Mande

      Articles written in Pramana – Journal of Physics

    • Determination of bond lengths in some compounds of rhenium from the x-ray LIII absorption discontinuity

      A V Pendharkar Chintamani Mande

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      The shapes and the fine structure of the x-ray LIII absorption discontinuity of rhenium have been studied in seven octahedral (K2ReCl6, K2ReBr6, (pyH)2ReCl6, (dipyH)2ReCl6, Re(dipy)Cl4, K3ReO2(CN)4 and ReO3) and three tetrahedral (KReO4, NH4ReO4 and NaReO4) compounds. The bond lengths in these compounds have been determined by applying Levy’s theory to the data on the fine structure associated with the edge beyond the molecular orbital region.

    • Plasmon excitation in the x ray absorption process

      Ashok Pimpale Chintamani Mande

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      A simple approach is developed to study the excitation of a plasmon due to valence electronic correlations in the x ray absorption process. Assuming a complete separation between the core and the valence electrons, we introduce the plasmons in the system Hamiltonian externally according to the Bohm-Pines collective formalism and carry out the corresponding canonical transformations to separate the x ray photonplasmon-electron term. According to our calculations, the relative intensity of the plasmon process with respect to the main absorption, which represents single particle excitations is 0·12 times the interelectronic separation measured in Bohr radii. The theoretical estimates of the plasmon intensity agree satisfactorily with the experimental values for the Mn K and the Re LIII absorption discontinuities.

      The shape of the plasmon absorption band resembles the main absorption edge, if the wave vector dependence of the plasmon frequency is neglected. The intensity of the second plasmon harmonic is about 3 per cent of the first plasmon satellite spectrum. The electron plasmon interaction modifies the shape of the plasmon spectrum.

    • The x-ray LIII absorption discontinuity of ytterbium in the metal and in some of its compounds

      Prabodhachandra Deshmukh Chintamani Mande

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      The shape and fine structure of the x-ray LIII absorption discontinuity of ytterbium (Z=70) has been studied in the pure metal and in several of its compounds. The shape and the near edge structure of the discontinuity in the metal reflects the band structure. A molecular orbital interpretation for the fine structure near the absorption edge has been proposed for the spectrum of the sesqui-oxide. The average bond lengths for the systems studied have been determined from the measurements on the fine structure employing Lytle’s and Levy’s methods and are compared with the available crystallographic data in the case of the metal, oxide and fluoride.

    • Modification of Lytle’s theory: Interpretation of the extended fine structure associated with LIII absorption discontinuity of some ytterbium systems

      Pranawa Deshmukh Prabodhachandra Deshmukh Chintamani Mande

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      In Lytle’s theory for the extended fine structure in x-ray absorption spectra, the potential at the boundary of the ‘equivalent sphere’ around the absorbing atom, having volume equal to that of the Wigner-Seitz cell is considered to be infinite. It has been observed that Lytle’s theory is applicable only in the case of metals and metallic systems. In the present paper the extended fine structure associated with the LIII absorption spectra of some systems of ytterbium is interpreted on the basis of Lytle’s model, modified by using a finite potential instead of an infinite one at the boundary of the equivalent sphere. The values of this potential are estimated for eight systems of ytterbium. It has been shown that there exists a correlation between the potentials and covalency of the compounds.

    • A study of Fermi level shifts in copper-gallium and copper-germanium alloys by x-ray absorption spectroscopy

      N R Lokhande Chintamani Mande

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      The K x-ray absorption discontinuities of copper, gallium and germanium in pure metals as well as in six copper-gallium and three copper-germanium alloys have been studied using a Cauchois-type bent crystal spectrograph. It is observed that in all the systems the K discontinuity of copper shifts towards the higher energy side, while the discontinuities of gallium and germanium shift to the lower energy side relative to their positions in the respective pure metals. The magnitudes of the shifts are found to increase with the decrease in the content of the absorbing atom in the alloys. The observed shifts are explained on the basis of the free-electron theory of metals and the rigid-band model for alloys.

    • Relative strengths of the competing multipoles in the K and L series x-ray spectra in theNR limit

      V S Edlabadkar Chintamani Mande

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      For most of the transitions of theK andL series x-ray spectra the ratio of the contributions of the competing multipoles, δ2, is independent of the radial matrix element in the non-relativistic limit. In the present paper calculations of δ2 are made in the non-relativistic limit which give the relative strengths of the two closely competing electric and magnetic multipoles. The dominant mode in the emission processes of the transitions in theK andL series x-ray spectra has been assigned on the basis of these calculations.

    • Raman effect in the x-ray region

      Ashok Pimpale Chintamani Mande

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      This paper presents a brief review of x-ray Raman scattering and some of our calculations on Raman scattered line shapes from light elements. We summarise the history of the Raman process in the x-ray region and present a detailed theory of the Raman scattering from an atomic many-electron system. Actual calculations of the Raman cross-section using this theory in single-particle approximation are given. The process of internal resonance Raman scattering is also discussed in the same formulation. The Raman cross-section is compared with the cross-sections of other x-ray scattering processes.

    • Bohr-Coster diagrams for multiply ionized states of light elements in the rangeZ = 10 to 20

      Lakshmi Natarajan A V Tankhiwale Chintamani Mande

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      Calculations in the L-S coupling approximation of the average total energies of various defect electron configurations with single or doubleK shell and varying number ofL shell vacancies for some light elements in the rangeZ = 10 to 20 are reported. The calculations show that the linear trend observed for normal Bohr-Coster diagrams (√E vsZ curves for the usual X-ray energy states) persists in the case of multiply ionized atomic states as well.

    • Spectroscopically determined electronegativity values for heavy elements

      Chintamani Mande Subha Chattopadhyay Prabodh C Deshmukh R Padma Pranawa C Deshmukh

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      A new scale of electronegativity based on X-ray spectroscopic data was earlier presented by Mande and others for the elements3Li to54Xe. The present paper reports an extension of this scale carried out for most of the heavier elements lying between55Cs and92U. The present approach is based on the physical interpretation of electronegativity of an atom as the attractive electrostatic force it exerts at a distance equal to its covalent radius. To estimate this force, experimental spectroscopic data have been employed. The merits of such an approach have been pointed out recently by Mullay and may be of interest in the context of the intimate relation found between electronegativity and superconducting transition temperature.

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