• Pradeep Kumar

      Articles written in Pramana – Journal of Physics

    • Collision cross-sections for scattering of electrons from NO molecule

      Arvind Kumar Jain Pradeep Kumar A N Tripathi

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      Electron-NO scattering is investigated in the energy range 2–1000eV by using a parameter-free spherical complex optical potential (SCOP) approach in the fixed nuclei approximation. The real part of the optical potential consists of three potentials namely, the static, the exchange and the polarization. For the imaginary part of the SCOP, we employ a semi-empirical model absorption potential. The molecular charge density function is calculated from a single-configuration molecular orbital based on Slater type orbitals. The various potential terms are then determined from these charge density functions. Calculations of the elastic (with and without absorption effects), total absorption, momentum transfer and differential cross-sections are obtained and compared with the available theoretical results and experimental measurements.

    • Potential energy curves for neutral and multiply charged carbon monoxide

      Pradeep Kumar N Sathyamurthy

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      Potential energy curves of various electronic states of CO$^{n+}$ ($0 \leq n \leq 6$) are generated at MRCI/CASSCF level using cc-pvQZ basis set and the results are compared with available experimental and theoretical data.

    • Temperature-dependent infrared reflectivity studies of multiferroic TbMnO3: Evidence for spin-phonon coupling

      Pradeep Kumar Surajit Saha C R Serrao A K Sood C N R Rao

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      We have measured near normal incidence far-infrared (FIR) reflectivity spectra of a single crystal of TbMnO3 from 10 K to 300 K in the spectral range of 50 cm-1 –700 cm-1. Fifteen transverse optic (TO) and longitudinal optic (LO) modes are identified in the imaginary part of the dielectric function $\varepsilon_{2} (\omega)$ and energy loss function Im($−1/\varepsilon(\omega))$, respectively. Some of the observed phonon modes show anomalous softening below the magnetic transition temperature $T_{N}$ ($\sim 46$ K). We attribute this anomalous softening to the spin-phonon coupling caused by phonon modulation of the superexchange integral between the Mn3+ spins. The effective charge of oxygen ($Z_{O}$) calculated using the measured LO–TO splitting increases below $T_{N}$.

    • Beam lifetime measurement and analysis in Indus-2 electron storage ring

      Pradeep Kumar A D Ghodke Gurnam Singh

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      In this paper, the beam lifetime measurement and its theoretical analysis are presented using measured vacuum pressure and applied radio frequency (RF) cavity voltage in Indus-2 electron storage ring at 2 GeV beam energy. Experimental studies of the effect of RF cavity voltage and bunched beam filling pattern on beam lifetime are also presented. An equation of stable beam current decay is evolved and this equation closely follows the observed beam current decay pattern. It shows that the beam is stable and the beam current decay is due to the beam–residual gas interaction (vacuum lifetime) and electron–electron interaction within a bunch (Touschek lifetime). The estimated vacuum, Touschek and total beam lifetimes from analytical formulations are also compared with the measured beam lifetime.

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