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[en] The efficiency of materials developed for solar energy and technological applications depends on the interplay between molecular architecture and light-induced electronic energy redistribution. The spatial localization of electronic excitations is very sensitive to molecular distortions. Vibrational nuclear motions can couple to electronic dynamics driving changes in localization. The electronic energy transfer among multiple chromophores arises from several distinct mechanisms that can give rise to experimentally measured signals. Atomistic simulations of coupled electron-vibrational dynamics can help uncover the nuclear motions directing energy flow. Through careful analysis of excited state wave function evolution and a useful fragmenting of multichromophore systems, through-bond transport and exciton hopping (through-space) mechanisms can be distinguished. Such insights are crucial in the interpretation of fluorescence anisotropy measurements and can aid materials design. Finally, this Perspective highlights the interconnected vibrational and electronic motions at the foundation of nonadiabatic dynamics where nuclear motions, including torsional rotations and bond vibrations, drive electronic transitions.
[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] The transverse decoherence of the kicked beam due to amplitude dependent tune shift and the linear and the second order chromaticity are studied. For the kicked beam the closed analytical expression for the beam centroid evolution in subsequent turns is obtained. Analysis of the kicked beam centroid signal on the machine optical characteristics is given.
[en] The excited electronic states of nearby molecules are in general coupled via Coulomb interaction even in the absence of wavefunction overlap. When two different organic molecules having a nearly resonant excited state are close enough, the dipole–dipole interaction can significantly affect their optical response. Even though they do not chemically interact, concerning their coupling to light, such molecules do not act independently, but rather as a ‘virtual heterodimer’ the response of which stems from, but is different from that of each molecule alone. We discuss here a simple and general model to estimate their resonant nonlinear susceptibilities. (paper)
[en] The six doublet and the two quartet electronic states ("2Σ"+(2), "2Σ"-, "2Π(2), "2Δ, "4Σ"-, and "4Π) of the OH radical have been studied using the multi-reference configuration interaction (MRCI) method where the Davidson correction, core-valence interaction and relativistic effect are considered with large basis sets of aug-cc-pv5z, aug-cc-pcv5z, and cc-pv5z-DK, respectively. Potential energy curves (PECs) and dipole moment functions are also calculated for these states for internuclear distances ranging from 0.05 nm to 0.80 nm. All possible vibrational levels and rotational constants for the bound state X"2Π and A"2Σ"+ of OH are predicted by numerical solving the radial Schroedinger equation through the Level program, and spectroscopic parameters, which are in good agreements with experimental results, are obtained. Transition dipole moments between the ground state X"2Π and other excited states are also computed using MRCI, and the transition probability, lifetime, and Franck-Condon factors for the A"2Σ"+ - X"2Π transition are discussed and compared with existing experimental values.
[en] To study the dynamics resonances of the Cl + HD reaction which was proposed to proceed via abstraction mechanism with no clear resonances, we perform dynamics calculations by the multiconfiguration time-dependent Hartree (MCTDH) method based on recently developed neural-networks potential energy surface (Science 347 (2015), 60). The HD molecule in (GS), (EX1), (EX2), and (EX3) states is used for the reactant. For GS, no distinctive resonance peak is found, while for EX1 two distinctive peaks at kinetics energies of and eV are investigated. These resonance peaks are well consistent with the previous results (Science 347 (2015), 60). Moreover, the present MCTDH calculations predict well-marked resonance peaks at , and eV for EX2 and EX3, which indicates that anticipation of the chemical bond softening model (Science 327 (2010), 1501) is confirmed in this work.
[en] In this paper we provide a detailed analysis of heat generation in a solid-state laser medium. The fractional thermal loadings are different for different physical processes in a laser medium, including the fluorescence process, stimulated emission, energy transfer up-conversion and excited-state absorption. Applying this theoretical analysis in a diode-end-pumped Nd:GdVO4 laser at 1342 nm, and using a simple and efficient method to measure the thermal loading of the solid-state laser medium presented, the experimental results are in good agreement with the theoretically calculated results. (paper)
[en] Vibrational excitation: The previous evaluation by Itikawa was based on an earlier evaluation by Brunger, Buckman, and Elford. Since these evaluations, new and more accurate experimental data have been published. For the vibrational excitation from the ground v=0 to the first excited level v=1 of N2, the recommended differential cross-sections are the ones measured by M. Allan. In this study, the differential cross-section for the v=0 → v=1 excitation was measured for scattering angles q=45o, 135o, and 180o for energies between 0.3 and 5.5 eV. The measured cross-section was not resolved rotationally, i.e. a sum over all rotational levels has been measured. The region of resonances between 1.9 and 3.7 eV is well resolved. The same study gave also the differential cross sections for the v=0 → v=1 excitation as a function of the scattering angle for several values of scattering energies, E=0.8, 1.988, and 5 eV. Rotational excitation: The previous evaluation by Itikawa for rotational excitation from j=0 → j=2 and from j=0 → j=4 used the data from an earlier evaluation by Brunger, Buckman, and Elford, which was based on swarm experiment data. Since these evaluations, another accurate theoretical calculation by Sulc et al. has been published. The resulting cross section for the j=0 → j=2 transition is in good agreement with the previous evaluation for energies <1 eV. Therefore, we recommend to keep the data recommended by Itikawa for the j=0 → j=2 and j=0 → j=4 transition. New measurements and/or theoretical calculations of the rotational excitation of N2 are needed for low (<1 eV) and higher (>1 eV) energies starting with ground and excited rotational level of N2
[en] The Kitaev-Heisenberg model is source of a topological quantum spin liquid with Majorana fermions and gauge flux excitations as fractional quasiparticles. The material -RuCl is composed of weakly van der Waals bound honeycomb layers of edge sharing RuCl octahedra which has recently emerged as a prime candidate for realising such physics. We studied -RuCl by means of thermal transport measurements, a valuable tool to probe elementary excitations of systems with low dimensional spin structure. While the in-plane, longitudinal heat transport is governed by heat conduction of phonons that strongly scatter off the magnetic excitations present in the system, studying the thermal Hall effect (Rhighi-Leduc effect) opens up a new path towards detecting a direct contribution of unconventional magnetic excitations to entropy transport. We have observed a sizeable transversal heat conductivity , the agreement of which with the theoretical predictions for the pure Kitaev model being suggestive of heat transport by fractionalised quasiparticles in -RuCl.
[en] The study of the spatially resolved physical and compositional properties of materials at the nanoscale is increasingly challenging due to the level of complexity of biological specimens such as those of interest in bioenergy production. Mode synthesizing atomic force microscopy (MSAFM) has emerged as a promising metrology tool for such studies. It is shown that, by tuning the mechanical excitation of the probe–sample system, MSAFM can be used to dynamically investigate the multifaceted complexity of plant cells. The results are argued to be of importance both for the characteristics of the invoked synthesized modes and for accessing new features of the samples. As a specific system to investigate, we present images of Populus, before and after a holopulping treatment, a crucial step in the biomass delignification process.