• Pranab Sarkar

      Articles written in Pramana – Journal of Physics

    • Bound state population and dissociation dynamics of a Morse oscillator with oscillating well-depth and driven by intense radiation: Perturbative and numerical studies

      Pranab Sarkar S P Bhattacharyya

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      Bound state population dynamics in a diatom modelled by an appropriate Morse oscillator with a time-dependent well-depth is investigated perturbatively both in the absence and presence of high intensity radiation. For sinusoidally oscillating well-depth, the population of themth bound vibrational level,Pmm(t), is predicted to be a parabolic function of the amplitude of the oscillation of the well-depth (ΔD0) at a fixed laser intensity. For a fixed value of ΔD0,Pmm(t) is also predicted to be quadratic function of the field intensity (ɛ0). Accurate numerical calculations using a time-dependent Fourier grid Hamiltonian (TDFGH) method proposed earlier corroborate the predictions of perturbation theory. As to the dissociation dynamics, the numerical results indicate that the intensity threshold is slightly lowered if the well-depth oscillates. Possibility of the existence of pulse-shape effect on the dissociation dynamics has also been investigated.

    • Tunneling through a time-dependent barrier — a numerical study

      Pranab Sarkar

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      We present a numerical investigation of quantum mechanical tunneling process in a double well potential with fluctuating barrier. The tunneling probability and rate are calculated for two cases in which (i) the height of the barrier is undergoing harmonic oscillation with frequency θ and (ii) the height of the barrier is undergoing random fluctuation with frequency θ. It is observed that in both cases, the quantum mechanical tunneling probability and rate exhibit a maximum as a function of the fluctuation frequency. The optimal frequency i.e. the frequency at which rate exhibits a maximum shows a strong isotopic mass effect.

    • Calculating pure rotational transitions of water molecule with a simple Lanczos method

      Pranab Sarkar

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      We have calculated pure rotational transitions of water molecule from a kinetic energy operator (KEO) with the z-axis perpendicular to the molecular plane. We have used rotational basis functions which are linear combinations of symmetric top functions so that all matrix elements are real. The calculated spectra agree well with the observed values.

    • Momentum densities and Compton profiles of alkali-metal atoms

      Pranab Sarkar Anupam Sarkar S N Roy B Talukdar

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      It is assumed that the dynamics of valence electrons of alkali-metal atoms can be well accounted for by a quantum-defect theoretic model while the core electrons may be supposed to move in a self-consistent field. This model is used to study the momentum properties of atoms from3Li to37Rb. The numerical results obtained for the momentum density, moments of momentum density and Compton profile are found to be in good agreement with the results of more detailed configuration-interaction calculations for the atom3Li. Similar results for11Na,19K and37Rb are compared with the corresponding Hartree-Fock-Roothaan values only, for want of data from other realistic calculations

    • Effects of barrier fluctuation on the tunneling dynamics in the presence of classical chaos in a mixed quantum-classical system

      Aparna Saha Bidhan Chandra Bag Pranab Sarkar

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      We present a numerical investigation of the tunneling dynamics of a particle moving in a bistable potential with fluctuating barrier which is coupled to a non-integrable classical system and study the interplay between classical chaos and barrier fluctuation in the tunneling dynamics. We found that the coupling of the quantum system with the classical subsystem decreases the tunneling rate irrespective of whether the classical subsystem is regular or chaotic and also irrespective of the fact that whether the barrier fluctuates or not. Presence of classical chaos always enhances the tunneling rate constant. The effect of barrier fluctuation on the tunneling rate in a mixed quantum-classical system is to suppress the tunneling rate. In contrast to the case of regular subsystem, the suppression arising due to barrier fluctuation is more visible when the subsystem is chaotic.

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