Molecular orbital diagram

Summary

A molecular orbital diagram, or MO diagram, is a qualitative descriptive tool explaining chemical bonding in molecules in terms of molecular orbital theory in general and the linear combination of atomic orbitals (LCAO) method in particular. A fundamental principle of these theories is that as atoms bond to form molecules, a certain number of atomic orbitals combine to form the same number of molecular orbitals, although the electrons involved may be redistributed among the orbitals. This tool is very well suited for simple diatomic molecules such as dihydrogen, dioxygen, and carbon monoxide but becomes more complex when discussing even comparatively simple polyatomic molecules, such as methane. MO diagrams can explain why some molecules exist and others do not. They can also predict bond strength, as well as the electronic transitions that can take place. History Qualitative MO theory was introduced in 1928 by Robert S. Mulliken and Friedrich Hund. A mathematical descri

Official source

https://en.wikipedia.org/wiki/Molecular_orbital_diagram

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The influence of external electric fields on charge reorganization energy in organic semiconductors

Weicong Huang, Hongguang Liu

Charge reorganization energies (k) of inter-ring carbon-carbon (IRCC) bond connected conjugated polycyclics are shown to exhibit an electric-field-driven anisotropic character. An external electric field parallel to the IRCC linker(s) reduces k while the field vertical to the molecular plane does the opposite. This anisotropic character can be modulated by introducing inter-ring noncovalent locks into appropriate sites.

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Interaction of carbon dioxide with Ni(110): A combined experimental and theoretical study

We present a combined experimental and theoretical study of the CO2 interaction with the Ni(110) surface. Photoelectron spectroscopy, temperature-programmed desorption, and high-resolution electron energy loss spectroscopy measurements are performed at different coverages and for increasing surface temperature after adsorption at 90 K with the aim to study the competing processes of CO2 dissociation and desorption. Simulations are performed within the framework of density functional theory using ab initio pseudopotentials, focusing on selected chemisorption geometries, determining the energetics and the structural and vibrational properties. Both experimental and theoretical vibrational frequencies yield consistent indications about two inequivalent adsorption sites that can be simultaneously populated at low temperature: short-bridge site with the molecular plane perpendicular to the surface and hollow site with the molecular plane inclined with respect to the surface. In both sites, the molecule has pure carbon or mixed oxygen-carbon coordination with the metal and is negatively charged and bent. Predicted energy barriers for adsorption and diffusion on the surface suggest a preferential adsorption path through the short-bridge site to the hollow site, which is compatible with the experimental findings. Theoretical results qualitatively support literature data concerning the increase of the work function upon chemisorption.

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Mikhail Churaev, Hairun Guo, Tobias Kippenberg, Junqiu Liu, Alexey Tikan, Rui Ning Wang

Collective effects leading to spatial, temporal or spatiotemporal pattern formation in complex nonlinear systems driven out of equilibrium cannot be described at the single-particle level and are therefore often called emergent phenomena. They are characterized by length scales exceeding the characteristic interaction length and by spontaneous symmetry breaking. Recent advances in integrated photonics have indicated that the study of emergent phenomena is possible in complex coupled nonlinear optical systems. Here we demonstrate that the out-of-equilibrium driving of a strongly coupled pair of photonic integrated Kerr microresonators ('dimer')-which, at the 'single particle' (that is, individual resonator) level, generate well-understood dissipative Kerr solitons-exhibits emergent nonlinear phenomena. By exploring the dimer phase diagram, we find regimes of soliton hopping, spontaneous symmetry breaking and periodically emerging (in)commensurate dispersive waves. These phenomena are not included in the single-particle description and are related to the parametric frequency conversion between the hybridized supermodes. Moreover, by electrically controlling the supermode hybridization, we achieve wide tunability of spectral interference patterns between the dimer solitons and dispersive waves. Our findings represent a step towards the study of emergent nonlinear phenomena in soliton networks and multimodal lattices. A pair of strongly coupled photonic microresonators shows nonlinear emergent behaviour, which can be understood by incorporating interactions in the theoretical description of nonlinear optical systems.

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