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The hydrogen atom

Xem 1-20 trên 39 kết quả The hydrogen atom
  • The heroine of this book is nature’s simplest atom, the hydrogen atom. With one exception—the helium atom—hydrogen is the mother of all atoms and molecules. The hydrogen atom consists of a single electron and a single proton; the proton is the nucleus of the hydrogen atom and serves as the electron’s anchor. The universe is teeming with hydrogen: every cubic centimeter of dark interstellar space, essentially void of any other known matter,1 contains a few atoms of hydrogen

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  • The hydrogen vibration was investigated to analyze its affect on the hydrogen adsorption on the missing row platinum surface (H/Pt(110)-(1x2) model) in the ultrahigh vacuum (UHV). The density functional theory (DFT) combined with the approximation oscillation of the hydrogen atom on the surface was used. When the hydrogen coverage Θ H on the surface is 100% (Θ H = 1 ML), and taking into account the vibrational effect, the bond formed at the edge of the first layer (short bridge) is the most stable site. The vibrational effect on the adsorption model H/Pt(110)- (1x2) is significant.

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  • Quantum Mechanics and the Hydrogen Atom, Many-Electron Atoms and Chemical Bonding, Molecular Orbitals, Spectroscopy, and Chemical Bonding,... as the main contents of the lesson lecture 9 "Tentative material to be covered for Exam 2". Invite you to consult the lesson for more documents serving the academic needs and research.

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  • Because of their apparent “simplicity” simple atoms present a great challenge and temptation to experts in various branches of physics from fundamental problems of particle physics to astrophysics, applied physics and metrology. This book is based on the presentations at the International Conference on Precision Physics of Simple Atomic Systems (PSAS 2002) whose primary target was to provide an effective exchange between physicists from different fields.

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  • Solar energy is radiant energy that is produced by sun. Everyday the sun radiates, or sends out, an enormous amount of energy. The sun radiates more energy in one second than people have used since the beginning of time! Where does the energy come from that constantly is being radiated from the sun? It comes from within the sun itself. Like other stars, the sun is a big ball of gases- mostly hydrogen and helium atoms. The hydrogen atoms in the sun’s core combine to form helium and generate energy in a process called nuclear...

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  • Antioxidant properties of ergothioneine (ESH) have been investigated via hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) mechanisms. Three new DFT methods including M06, WB97XD and TPSSTPSS at the 6-311++G(2df,2p) basis set were used to compute the thermochemical parameters of ESH in the gas phase.

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  • Our study includes the optimization of the geometries, the calculation of the binding energies and relevant vibrational frequencies along with a natural bond orbital analysis including the charges on the different atoms, the occupation of selected antibonding orbitals and the hyperconjugation energies.

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  • Molecules, small structures composed of atoms, are essential substances for lives. However, we didn’t have the clear answer to the following questions until the 1920s: why molecules can exist in stable as rigid networks between atoms, and why molecules can change into different types of molecules. The most important event for solving the puzzles is the discovery of the quantum mechanics. Quantum mechanics is the theory for small particles such as electrons and nuclei, and was applied to hydrogen molecule by Heitler and London at 1927.

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  • A covalent bond results when two atoms share electrons in such a way that each atom has an octet of electrons in the outer shell. In a hydrogen atom, the outer shell is complete when it contains two electrons. If hydrogen is in the presence of a strong electron acceptor, it gives up its electron to become a hydrogen ion (H+). But if this is not possible, hydrogen can share with another atom and thereby have a completed outer shell. For example, one hydrogen atom will share with another hydrogen atom. Their two orbitals overlap,...

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  • Galloylated and nongalloylated catechin conjugates with cysteine deriva-tives have been synthesized and evaluated for their capacity to scavenge free radicals and to influence crucial functions (cell cycle, apoptosis) in HT29 colon carcinoma cells. We show that the nonphenolic part of the molecule modified the capacity of catechins to donate hydrogen atoms and to transfer electrons to free radicals.

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  • Identify the four major elements; distinguish between the following pairs of terms: neutron and proton, atomic number and mass number, atomic weight and mass number; distinguish between and discuss the biological importance of the following: nonpolar covalent bonds, polar covalent bonds, ionic bonds, hydrogen bonds, and van der Waals interactions.

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  • The structure and dynamics of proteins and enzymatic activity is intrinsically linked to the strength and positions of hydrogen bonds in the system.[1] A hydrogen bond results from an attractive force between an electronegative atom and a hydrogen atom.[2] The hydrogen is attached to a strongly electronegative heteroatom, such as oxygen or nitrogen, termed the hydrogen- bond donor. This electronegative atom decentralizes the electron cloud around the hydrogen nucleus, leaving the hydrogen atom with a positive partial charge.

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  • Many biological C-H activation reactions exhibit nonclassical kinetic isotope effects (KIEs). These nonclassical KIEs are too large (kH/kD 7) and/or exhibit unusual temperature dependence such that the Arrhenius prefactor KIEs (AH/AD) fall outside of the semiclassical range near unity. The focus of this minireview is to discuss such KIEs within the context of the environmentally coupled hydrogen tunneling model.

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  • The VATLY radio telescope has been used to draw the map of atomic hydrogen gas in the disk of the Milky Way. Effects resulting from its differential rotation, its cloud and arm structure and the presence of a dark matter halo have been observed.

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  • The morphology of the ZnO microbelt sensor was examined by field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The diameter and length of the microbelt were 5 µm and 220 µm, respectively. The porphyrin islands height was few tens of nanometers. The fabricated sensor showed a good response to hydrogen at quite low working temperature. The mechanism of the hybrid sensor needs to be studied further in future.

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  • The methyl a-D-mannopyranoside molecule is bound in the Cl chair conformation 8.7 A from the calcium-binding site and 12.8 A from the transition metal-binding site. A network of seven hydrogen bonds connects oxygen atoms 0-3, 04, 0-5 and 0-6 of the mannoside to residues Asnl4, Leu99, TyrlO0, Asp208 and Arg228. 0-2 and 0-1 of the mannoside extend into the solvent. 0-2 is hydrogenbonded through a water molecule to an adjacent asymmetric unit.

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  • To investigate the H2 purification mechanism of V membranes, we studied the adsorption, dissociation, and diffusion properties of H in V, an attractive candidate for H2 separation materials. Our results revealed that the most stable site on the V (1 0 0) surface is the hollow site (HS) for both adsorbed H atoms and molecules. As the coverage range increases, the adsorption energy of H2 molecules first decreases and then increases, while that of H atoms remains unchanged.

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  • The goal of study is to predict the free radical scavenging activity of five compounds via two widely accepted mechanisms: hydrogen atom transfer (HAT) mechanism and single electron transfer (SET). The intrinsic parameters of the studied compounds including bond dissociation enthalpies (BDE), ionization potential (IP) and electron affinity (EA) were calculated by density functional theory (DFT) approach at the M05- 2X/6-31+G(d) level of theory in the gas phase.

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  • This work presents an analytic methodology to produce such a covariance matrix-associated to the water model developed at the Atomic Center of Bariloche (Centro Atomico Bariloche, CAB, Argentina).

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  • The second major aim of this work is to understand the antioxidant mechanisms of the diphenylamines. The potential energy surfaces (PES) of reactions between the substituted diphenylamines with CH3OO• radical were calculated at M05-2X/6-311++G(d,p) level of theory. Rate constants for hydrogen atom transfer processes at the NH bond were also computed at the same level of theory using the conventional transition state theory (TST).

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