Results 1 - 10 of 4115
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[en] Highlights: • We examined the attainment of the Conical Intersection (CI) in Hipoxantine (Hx). • Charge transfer in the molecule is very important in the evolution of S0 and S1. • Aromaticity impairment and push pull systems in Hx are crucial in attaining its CI. • QTAIM offers valuable tools to study the photostability of nucleobases. We analyzed the evolution of the electron density across the S0 and S1 states potential energy curves of hypoxanthine (Hx) using the Quantum Theory of Atoms in Molecules (QTAIM). Examination of QTAIM energies and electronic populations indicates that charge transfer processes are important in the stabilization of the S1 state towards the Conical Intersection (CI) which confers to Hx its photostability. Our results point that the rise of energy of the S0 state approaching the CI is accompanied by a loss of aromaticity of hypoxanthine. Overall, the analyses presented herein give important insights on the photostability of nucleobases.
[en] Highlights: • High resolution L1-L2,3M Coster-Kronig spectra in Ar are obtained by electron impact. • Many features are due to the autoionizing decay of neutral doubly excited states. • Energy analysis of ejected electrons ruled out hypothesis of the state origins. - Abstract: The ejected electron spectra between 25 and 56 eV kinetic energy in Ar have been measured at several electron impact energies. When the incident energy is above the Ar 2s ionization potential the peaks due to the L1-L2,3M1 and L1-L2,3M2,3 Coster-Kronig (CK) transitions are expected to occur in this region of kinetic energy, but we observe a series of other narrow structures that overlap and sometime dominate the spectrum due to the CK transitions. These features have been attributed to the autoionizing decay of inner valence doubly excited states to the Ar + ground state.
[en] The relativistic Multi-Reference Møller–Plesset (MR-MP) many-body perturbation theory was applied to calculate the energies of all excited states within the 3s3p, , 3s3d, 3p3d and configurations for every ion of the Mg isoelectronic sequence (). The results are compared with previous calculations and available experimental data. The MR-MP excitation energies agree with experiment typically within 100 ppm over a wide range of , particularly for mid- and high-range . Experimental data for highly charged ions in this isoelectronic sequence are limited and the complete and accurate dataset presented here is expected to ease the identification process upon measurements.
[en] A unique detector which is selectively sensitive to low energy metastable atoms, has been used to study the production of ground state N (2P) atoms following collisions of low energy (0–200 eV) electrons with molecular nitrogen. Time-of-flight techniques have revealed the existence of at least two distinct mechanisms yielding this dissociation product. Released kinetic energies in the dissociation have allowed positioning of the parent molecular states in the Franck–Condon region. This, together with excitation probability curves, has allowed probable parent states, such as B′ b′ and C′ 3Πu, to be identified making use of recent theoretical calculations. Both direct and pre-dissociation processes are shown to be involved. (paper)
[en] Highlights: • CaH is an important molecule in astrophysics. • We studied the low-lying electronic states of CaH at the MRCI level of theory. • Accurate transition dipole moments and lifetimes were computed for several excited states. • Perturbations in the A2Π and B2Σ+ states have been discussed. Ab initio potential energy curves have been calculated for the X2Σ+, A2Π, B2Σ+, 12Δ, E2Π and D2Σ+ states of CaH using the multi-reference configuration interaction method with large active space and basis sets. Transition dipole moments were calculated at Ca–H distances from 2.0 a0 to 14.0 a0, and excited state lifetimes were obtained. Our theoretical transition dipole moments can be combined with the available experimental data on the X2Σ+, A2Π and B2Σ+ states to calculate Einstein A coefficients for all rovibronic transitions of CaH appearing in solar and stellar spectra.
[en] The paper presents an innovative way to improve the efficiency of solar energy. The requirements for the two components of the solar cell (the substrate material and the nature of the p-n junction) are determined. The necessity of nanotechnological preparation of the solar cell substrate is shown. The conditions under which technical silicon can be considered as a substrate are determined. A physical picture of the growth process of nanoclusters on the substrate surface based on the fundamental physical effect of self-organization of semiconductor systems is given. The least acceptable parameters of the nanocluster material are determined. The mechanism of the formation process of nanoheterogeneous structure is determined. The special role solar cell nanocomponents is revealed. (authors)
[en] The effect of vibrational excitation on reaction C+SH (v = 0–20, j = 0) → S+CH, H+CS is investigated on the excited potential energy surface of HCS(A2A″) by the quasi-classical trajectory method. The obtained reaction probability, total integral cross section (ICS), and the impact parameter show that the influence of vibration excitation presents different characteristics on different reaction channels. The vibrational state-resolved ICSs, differential cross sections as well as two-angle distribution functions P(θr), P(ϕr) of products for different vibrational quantum numbers of reactant are investigated. These results show that (i) the products have obvious forward–backward scattering feature; (ii) for different reactions, the distribution P(θr) varies with vibrational quantum number of reactant; (iii) at high vibrational excitations of the reactant, the insertion mechanism becomes apparent in this reaction, so the product molecules are more positively oriented along the positive direction of the scattering plane. Graphical abstract: .
[en] Highlights: • The excited states of PbH were calculated with MRCI+Q method. • Spin-orbit coupling effect was taken into consideration in the calculations. • Spectroscopic constants of bound states of PbH were evaluated. • The dipole moments were used to reveal the ionic characteristics of the states. • Radiative lifetimes of 14Σ–1/2 and 14Σ–3/2 states of PbH were determined. The 10 Ʌ-S states associated with the lowest four dissociation limits of PbH radical have been studied utilizing configuration interaction method. For better accuracy, the Davidson correction, core-valence correlation and spin-orbit coupling effects are included. The potential energy curves of 10 Ʌ-S states and 18 Ω states have been obtained and characterized. The computed dipole moments of 10 Ʌ-S states are used to reveal the ionic characteristics of the Ʌ-S states. Finally, the transitional dipole moments of several bound Ω states and lifetimes of vibrational states trapped in excited bound Ω states are determined.
[en] We consider a non-relativistic two-dimensional (2D) hydrogen-like atom in a weak, static, uniform magnetic field perpendicular to the atomic plane. Within the framework of the Rayleigh-Schrödinger perturbation theory, using the Sturmian expansion of the generalized radial Coulomb Green function, we derive explicit analytical expressions for corrections to an arbitrary planar hydrogenic bound-state energy level, up to the fourth order in the strength of the perturbing magnetic field. In the case of the ground state, we correct an expression for the fourth-order correction to energy available in the literature.
[en] We study the charge and heat transport in a normal metal/superconductor (NS) junction of the tilted anisotropic Dirac cone material borophane, using the extended Blonder–Tinkham–Klapwijk formalism. In spite of the large mismatch in the Fermi wave vector of the normal metal and superconductor sides of the borophane NS junction, the electron–hole conversion happens with unit probability at normal incidences. Furthermore, in the heavily doped superconducting regime, for heavily doped normal borophane, the electron–hole conversion happens with unit probability, at almost any incident angle. Finding the dependence of the differential Andreev conductance on the Fermi energy and excitation energy gives us a handle to distinguish specular from retro Andreev reflection. We numerically find that, independent of the Fermi energy, the temperature dependence of the differential thermal conductance in borophane can be modelled as an inverse Gaussian function, reflecting the d-wave symmetry of the borophane superconductor. We propose a scheme for achieving negative differential thermal conductance, as a key building block of thermal circuits, at intermediate Fermi energies. Our findings will have potential applications in developing borophane-based thermal management and signal manipulation mesoscopic structures such as heat transistors, heat diodes, and thermal logic gates. (paper)