Articles written in Pramana – Journal of Physics

    • Systematic trends in the line strengths and radial matrix elements of E1 transitions in the Be isoelectronic sequence

      Anand Bharadvaja K L Baluja

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      Line strengthS and radial matrix elementσ for the dipole allowed transitions withinn=2 complex of ions in the Be isoelectronic sequence have been fitted in the formsZ2S=A+B/(Z − C) andZσ=A′ + B′/(Z − C′). The constantsA, B, C andA′, B′, C′ have been calculated by employing a non-linear least square method. The relevant data forS andσ have been taken from calculations which includes correlation effects. It is shown that the fitted yalues ofA andA′ are in excellent accord with their hydrogenic values (Zα) provided that we express the zeroth-order wavefunction of the ground state 1s22s21S as a quantum-mechanical admixture of the Hartree-Fock (HF) state 1s22s21S and the near-degenerate state 1s22p21S.

    • Low-energy electron impact cross-sections and rate constants of $NH_2$


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      This systematic study reports various electron impact cross-sections, rate constants and transport properties of $NH_2$ radical in the low-energy limit. The collision study is based on $R$-matrix formalism and involves the use of various scattering models employing different active spaces. Both electron excited inelasticcross-sections and resonances are found influenced by correlation and polarization effects. The non-relativistic molecular bremsstrahlung radiation cross-section for soft photons, binary encounter Bethe model-based ionization cross-sections and a few molecular properties of the target radical are also reported. The present calculations are found to be in agreement with the available results. This theoretical study provides a pathway to understand collision dynamics and generates data required in various fields of applied physics.

    • Electron-impact cross-sections of atmospherically relevant amines from intermediate to 5000 eV energy range


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      The amines are major source of environment pollutants emitted in atmosphere from variousanthropogenic sources. The non-thermal plasma (NTP)-based technology has proved successful in controlling the emitted amines reaching the atmosphere. The efficient NTP reactors rely on accurate electron–molecule collision data. The electron impact cross-sections are thus obtained for a few amines from ionisation threshold to 5000 eV using the single centre expansion (SCE) formalism. Themolecular wave function of each target is obtained from themulticentre expansion of the Gaussian-type orbitals within a single determinant Hartree–Fock self-consistent field scheme. The expansion of wave function, density and potential is carried out at the centre of mass of the molecules. The interaction potential included to model the electron interaction in the target comprises static, correlation polarisation and exchange types of potentials. The elastic cross-sections are obtained after solving the coupled scattering equations using Volterra integral form. The inelastic effects contributing to electron–molecule scatteringare approximated by the ionisation cross-sections. The total cross-sections obtained after summing the elastic and ionisation cross-sections are in good agreement with the available data. We have also tried to explain the effect of polarisation potential on scattering cross-sections. A semiempirical formula based on the spatial extent of the molecule is proposed to estimate the cross-sections for the homologous series of amine molecules.

    • A study of electron scattering from O3 and its isovalent molecules from0.1 to 5 keV


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      The electron scatterings from isovalent molecules like O$_3$, S$_3$, OSO and SOS are studied using single centre expansion (SCE) approximation. The elastic differential cross-sections, integral and momentum transfer cross-sections are computed for these targets from ionisation threshold to 5 keV. The molecular wave functions of the targets were obtained from the multicentre expansion of the Gaussian-type orbitals within the single determinant Hartree–Fock self-consistent field scheme. The multipole expansion of the target at the centre of mass includes the dipole and quadrupole terms. The target interactions are modelled within the local potential approximation and consist of static, correlation-polarisation and exchange effects. The results are in good agreement with the available experimental and theoretical results. The SCE results match smoothly near the ionisation threshold with the {ab-initio} R-matrix results. This helped in estimating the scattering cross-section data from 0.1 to 5 keV energy. The totalcross-sections obtained by summing the elastic and inelastic cross-sections are also in excellent agreement with the available results. The scattering study from isovalent molecules further helped in understanding the effects of dipole moment, polarisation and geometrical size while evaluating the collision problem.

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