• Volume 18, Issue 3

      March 1982,   pages  225-294

    • Dissociation energies for the electronic ground states of BeCl, GaH and LiH

      N Rajamanickam U D Prahllad B Narasimhamurthy

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      The dissociation energies of the diatomic molecules BeCl, GaH and LiH have been computed by fitting empirical potential functions to the true potential energy curves for the electronic ground states of the molecules. The Lippincott three-parameter potential function, the five-parameter Hulburt-Hirschfelder potential function and the Szöke and Baitz electronegativity potential function have been used. The estimated dissociation energiesD00 are 4·50, 3·09 and 2·94 eV for BeCl, GaH and LiH respectively. These values compare well with the experimental values.

    • Relative vibrational transition probabilities in the (B3πgA3Σu+) system of nitrogen for Hulbert-Hirschfelder oscillator model

      R S Godge Sharada Itagi V V Itagi

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      Hulbert-Hirschfelder (h-h) potential function has been used to obtain the relative vibrational transition probabilities for the observed bands of the first positive system of nitrogen molecule. The vibrational wavefunctions have been calculated by solving the Schrödinger equation by the method due to Langer, at low vibrational quanta and by thewkb method at high vibrational quanta. It is established that theh-h potential is superior to the often used Morse potential function for the transition under consideration.

    • On the non-existence of hydrodynamic solution of surface plasmons at the bimetallic interface

      C Uberoi J Reyes

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      It is shown that for an abrupt bimetallic interface a hydrodynamic solution for interface plasmons does not exist. It appears that this result is valid irrespective of the choice of of the additional boundary condition, thereby suggesting a careful look at the use of usual hydrodynamic equations for a bimetallic interface.

    • A Mössbauer study of hyperfine interaction in the systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4

      V K Singh R Chandra S Lokanathan

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      A Mössbauer study of systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4 for values ofx=0·1, 0·5, 1·0 andy ranging from 0·1 to 2·0 in steps of 0·2 have been made. At room temperature samples fory values ranging in between 0·1 to 0·5 exhibit paramagnetic behaviour while all spectra for values ofy between 0·6 to 0·8 show relaxation effects. Well-defined hyperfine Zeeman spectra are observed for all the samples withy>0·8 and resolved in two sextets corresponding to octahedral and tetrahedral site symmetries and a central doublet probably due to the presence of super-paramagnetic particles in the system. The hyperfine field at57Fe nucleus reduces with decreasing iron cobalt and nickel concentration. These observations have been explained in terms of site preference of cations and exchange interactions.

    • Heat capacity of MnBr2·4H2O near the antiferromagnetic transition temperature

      S N Bhatia

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      Heat capacity of MnBr2·4H2O has been measured in the critical region around the Neel temperature. The data can be fitted, over a restricted range of |t|⩽10−2, to the asymptotic power law. The critical exponents and the amplitudesA andA′ are not consistent with any theoretic predictions. However when scaling constraints are imposed, their values agree with the parameters of Ising model. Corrections to scaling are necessary to extend the range of the fit to |t|>10−2. The correction terms are asymmetric giving −1·15±0·25 as the ratio of the amplitudes of the lowest order correction terms,D andD′ above and belowTc. This value is in agreement with the recent predictions of the renormalisation group theory.

    • On certain correspondences among various coupled-cluster theories for closed-shell systems

      Sourav Pal M Durga Prasad Debashis Mukherjee

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      In this paper certain correspondences have been shown among various formulations of coupled-cluster theories for many electron closed-shell systems. Specifically it is shown that (i) the energy functional using unitary ansatz of the form exp (TT+) is exactly sameorder by order inT with the size-consistent energy functional 〈ψ|H|ψ〉/〈ψ|ψ〉 recently obtained by us in coupled-cluster framework; (ii) in the framework of unitary ansatz of the form exp (TT+), both non-variational and variational approaches lead to identical equations upto any given order inT andT+ inTT2 approximation; (iii) variational procedure using our size-consistent energy functional or using the functional obtained in the framework of unitary ansatz (as envisaged by Kutzelnigg) leads to energy in both cases, inTT2 approximation, for a total of quadratic powers inT andT+, same as Cizek’s linearised coupled pair many electron theory energy; (iv) in case of practical calculation of the energy through the variational procedures using our size-consistent energy functional and the functional in unitary ansatz framework, there is a loss of upper bound.

    • Incoherent scattering functions of 145 keV gamma rays by K-shell electrons in Y, Ag and Au

      A Raghava Rao SS Ramana Reddy K Premchand K L Narasimham K Parthasaradhi V Lakshminarayana

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      The values of incoherent scattering functions are determined experimentally for 145 keV gamma rays in elements Au, Ag and Y at scattering angles 40°, 70° and 100°, using a x-ray gamma coincidence technique. The corresponding theoretical values are obtained from the tabulations of Hubbellet al, and computed from the models of Jauch and Rohrlich and Shimizuet al. A comparison between the theoretical and experimental results showed that the non-relativistic approach adopted in the theory of Shimizuet al is inapplicable to the present cases. A gross agreement is noticed between the present experimental results and the other theoretical values.

    • Coherent pion-photoproduction by deuterons at intermediate energies

      V S Bhasin V K Gupta J D Anand

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      Non-relativistically exact single scattering calculations for coherent pion photoproduction by deuterons at intermediate photon energies (200 MeV to 500 MeV) are presented. For the two-bodyγNπN process we use the well-known dispersion theoretic model by Chewet al and for the deuteron wave-functions we employ the Yamaguchi and the two term Gaussian wave-function. We find that while both the wavefunctions reproduce the deuteron e.m. form factor reasonably well, the results for the pion photoproduction cross-section show, however, a sensitive dependence on their detailed forms. The angular distributions at various energies are found to have considerable variations from the usual impulse approximation calculations but tend to improve the agreement with the data in a large kinematical region.

    • Bag like potential and quarkonium

      Tej K Zadoo G Q Sofi

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      We discuss the properties of charmonium in the frame work of a bag like potential and show that the upsilon and charmonium spectra can be fitted by a common potential.

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