Articles written in Pramana – Journal of Physics
Volume 1 Issue 2 August 1973 pp 104-108 Solids
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.
Volume 1 Issue 3 September 1973 pp 147-154 Solids
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.
Volume 2 Issue 3 March 1974 pp 138-147 Solids
The shape and fine structure of the x-ray LIII absorption discontinuity of ytterbium (
Volume 6 Issue 5 May 1976 pp 305-311 X-Ray Crystallography
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.
Volume 17 Issue 1 July 1981 pp 1-12 Solid State Physics
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.
Volume 20 Issue 3 March 1983 pp 175-182 Atomic Physics
For most of the transitions of the
Volume 23 Issue 3 September 1984 pp 279-295 Atomic Physics
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.
Volume 29 Issue 3 September 1987 pp 253-260 Atomic And Molecular Physics
Calculations in the L-S coupling approximation of the average total energies of various defect electron configurations with single or double
Volume 35 Issue 4 October 1990 pp 397-403
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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