• Volume 50, Issue 5

      May 1998,   pages  355-462

    • Excitation of 31,3P and 31,3D states of helium from the ground 11S state by electrons and positrons

      Surbhi Verma Rajesh Srivastava

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      A systematic theoretical study is carried out for the electron and positron impact excitation of the 31,3P and 31,3D states of helium from the ground 11S state. The results are reported for the differential cross sections, Stokes parameters and alignment and orientation parameters. To calculate the scattering amplitude which relate these parameters, a distorted wave approximation theory with different choices of distortion potential has been used. The results are compared with available theoretical and experimental data in the energy range of 40–100eV.

    • Dissociation energy of diatomic molecules

      Sarvpreet Kaur C G Mahajan

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      The dissociation energy of twelve diatomic molecules has been determined by fitting four-parameter potential functionU(r)=De[[1−exp{−b(rre)}]/ [1−Cexp{−b(rre)}]]2 to the true Rydberg-Klein-Rees (RKR) curves for their fifteen electronic states using the mean square deviation as the criterion for the selection of the best fit. Average deviation ofDe has been found to be 2.7% as compared to 20.5% obtained with Lippincott’s potential function for these molecules. In addition the anharmonocity constantωexe has also been calculated for the same electronic states yielding average mean deviation 8.9%.

    • Stark splitting and energy transfer between Dy3+-Ho3+ and between Tb3+-Er3+ in calcium-lithium borate glass

      Brajesh Sharma V B Singh D K Rai S B Rai

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      Fluorescence spectrum of Dy3+, Dy3+-Ho3+, Tb3+ and Tb3+-Er3+ doped in calibo glass have been studied using Ar+ and excimer lasers. Non-radiative energy transfer from trivalent dysprosium and terbium (donors) to holmium and erbium (acceptors) respectively has been observed on the basis of decrease in the life time of the levels and reduction in fluorescence intensity of Dy3+ and Tb3+ on increasing Ho and Er concentrations. The interaction mechanism of donor and acceptor ions is found to be dipole-dipole in both cases. Various parameters such as donor-acceptor distances, non-radiative energy transfer efficiency (η) and energy transfer probability (Pda) have been computed. Stark splitting have also been marked in several intense transition of the two.

    • Laser optogalvanic spectroscopy of argon in the wavelength region 605–740 nm

      R C Sharma T Kundu S N Thakur

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      Two-photon optogalvanic transitions in Ar glow discharge with Nd: YAG laser pumped dye laser excitation in the frequency range 13520–16520 cm−1 has been studied using linear and circular polarization. The intensities of two-photon optogalvanic transitions are very sensitive to changes in the incident laser power which is not the case with one-photon transitions. Intensity ratio for circular and linear polarized light for two photon transitions 6s′[1/2]°1←4s[3/2]°2, 6s′[1/2]°0←4s[3/2]°2, and 5d[1/2]°0←4s[3/2]°2, 5d[1/2]°1←4s[3/2]°2 are quite different from the other two-photon transitions. This has been explained as due to near one photon resonance of 4p′[3/2]1 level for the first pair and 4p′[1/2]1 for the second pair of transitions. The ratio of optogalvanic intensity for circular to linear polarized light has been theoretically estimated and compared with the observed results.

    • An electrostatic charge state selector for ion-atom collisions: Design, spectral line-shapes and performance

      Amal K Saha K V Thulasi Ram L C Tribedi W A Fernandes S D Narvekar V Nanal M B Kurup K G Prasad P N Tandon

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      An electrostatic charge state selector has been constructed for charge transfer studies in ion atom collisions. Its design and performance have been discussed illustrating with examples of some data taken using heavy ion beams from the pelletron accelerator. Expressions for the determination of charge state fractions from the observed charge spectrum in voltage scanning mode of operation and also the line shapes have been discussed analytically in detail.

    • Total electron scattering cross sections for carbon dioxide at low electron energies

      P Rawat K P Subramanian Vijay Kumar

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      Absolute total electron scattering cross sections for carbon dioxide have been measured at low electron energies using a photoelectron source. The measurements have been carried out at 27 electron energies varying from 0.91–9.14 eV with an accuracy of ±3%. The cross sections obtained in the present experiment have been compared with other measurements and theoretical computations.

    • Magnetization of high-Tc superconductors

      B Kalta K K Nanda

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      We have tried to understand the field dependence of magnetization of high temperature superconductors in the light of phenomenological theory. Especially, the field dependence of dM/d lnB of polycrystalline Bi(2212) is understood by incorporating the overlap of vortices in the London theory.

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      Posted on July 25, 2019

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