Related Research Articles
In chemistry, a hydrogen bond is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Such an interacting system is generally denoted Dn−H···Ac, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are the second-row elements nitrogen (N), oxygen (O), and fluorine (F).
Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium. Unlike hydrogen, the system has no protons. The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending on the relative spin states. The energy levels of the two particles are similar to that of the hydrogen atom. However, because of the reduced mass, the frequencies of the spectral lines are less than half of those for the corresponding hydrogen lines.
The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Four widely used definitions of atomic radius are: Van der Waals radius, ionic radius, metallic radius and covalent radius. Typically, because of the difficulty to isolate atoms in order to measure their radii separately, atomic radius is measured in a chemically bonded state; however theoretical calculations are simpler when considering atoms in isolation. The dependencies on environment, probe, and state lead to a multiplicity of definitions.
Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.
In physics, quantum tunnelling, barrier penetration, or simply tunnelling is a quantum mechanical phenomenon in which an object such as an electron or atom passes through a potential energy barrier that, according to classical mechanics, the object does not have sufficient energy to enter or surmount.
Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule.
A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number, n. The higher the value of n, the farther the electron is from the nucleus, on average. Rydberg atoms have a number of peculiar properties including an exaggerated response to electric and magnetic fields, long decay periods and electron wavefunctions that approximate, under some conditions, classical orbits of electrons about the nuclei. The core electrons shield the outer electron from the electric field of the nucleus such that, from a distance, the electric potential looks identical to that experienced by the electron in a hydrogen atom.
Kaonic hydrogen is an exotic atom consisting of a negatively charged kaon orbiting a proton.
An electron bubble is the empty space created around a free electron in a cryogenic gas or liquid, such as neon or helium. They are typically very small, about 2 nm in diameter at atmospheric pressure.
The hydrogen anion, H−, is a negative ion of hydrogen, that is, a hydrogen atom that has captured an extra electron. The hydrogen anion is an important constituent of the atmosphere of stars, such as the Sun. In chemistry, this ion is called hydride. The ion has two electrons bound by the electromagnetic force to a nucleus containing one proton.
Bond order potential is a class of empirical (analytical) interatomic potentials which is used in molecular dynamics and molecular statics simulations. Examples include the Tersoff potential, the EDIP potential, the Brenner potential, the Finnis–Sinclair potentials, ReaxFF, and the second-moment tight-binding potentials. They have the advantage over conventional molecular mechanics force fields in that they can, with the same parameters, describe several different bonding states of an atom, and thus to some extent may be able to describe chemical reactions correctly. The potentials were developed partly independently of each other, but share the common idea that the strength of a chemical bond depends on the bonding environment, including the number of bonds and possibly also angles and bond lengths. It is based on the Linus Pauling bond order concept and can be written in the form
Positronium hydride, or hydrogen positride is an exotic molecule consisting of a hydrogen atom bound to an exotic atom of positronium. Its formula is PsH. It was predicted to exist in 1951 by A Ore, and subsequently studied theoretically, but was not observed until 1990. R. Pareja, R. Gonzalez from Madrid trapped positronium in hydrogen laden magnesia crystals. The trap was prepared by Yok Chen from the Oak Ridge National Laboratory. In this experiment the positrons were thermalized so that they were not traveling at high speed, and they then reacted with H− ions in the crystal. In 1992 it was created in an experiment done by David M. Schrader and F.M. Jacobsen and others at the Aarhus University in Denmark. The researchers made the positronium hydride molecules by firing intense bursts of positrons into methane, which has the highest density of hydrogen atoms. Upon slowing down, the positrons were captured by ordinary electrons to form positronium atoms which then reacted with hydrogen atoms from the methane.
The dihydrogen cation or hydrogen molecular ion is a cation with formula H+
2. It consists of two hydrogen nuclei (protons) sharing a single electron. It is the simplest molecular ion.
A trojan wave packet is a wave packet that is nonstationary and nonspreading. It is part of an artificially created system that consists of a nucleus and one or more electron wave packets, and that is highly excited under a continuous electromagnetic field.
The timeline of quantum mechanics is a list of key events in the history of quantum mechanics, quantum field theories and quantum chemistry.
In chemistry, ice rules are basic principles that govern arrangement of atoms in water ice. They are also known as Bernal–Fowler rules, after British physicists John Desmond Bernal and Ralph H. Fowler who first described them in 1933.
Bond softening is an effect of reducing the strength of a chemical bond by strong laser fields. To make this effect significant, the strength of the electric field in the laser light has to be comparable with the electric field the bonding electron "feels" from the nuclei of the molecule. Such fields are typically in the range of 1–10 V/Å, which corresponds to laser intensities 1013–1015 W/cm2. Nowadays, these intensities are routinely achievable from table-top Ti:Sapphire lasers.
The hydrodynamic quantum analogs refer to experimentally observed phenomena involving bouncing fluid droplets over a vibrating fluid bath that behave analogously to several quantum mechanical systems.
Quantum microscopy allows microscopic properties of matter and quantum particles to be measured and imaged. Various types of microscopy use quantum principles. The first microscope to do so was the scanning tunneling microscope, which paved the way for development of the photoionization microscope and the quantum entanglement microscope.
The quantum tunneling of water occurs when water molecules in nanochannels exhibit quantum tunneling behavior that smears out the positions of the hydrogen atoms into a pair of correlated rings. In that state, the water molecules become delocalized around a ring and assume an unusual double top-like shape. At low temperatures, the phenomenon showcases the quantum motion of water through the separating potential walls, which is forbidden in classical mechanics, but allowed in quantum mechanics.
References
- ↑ Löwdin, P. O. (1963). "Proton Tunneling in DNA and its Biological Implications". Rev. Mod. Phys. 35 (3): 724–732. Bibcode:1963RvMP...35..724L. doi:10.1103/RevModPhys.35.724.
- ↑ Castro Neto, A. H.; Pujol, P.; Fradkin, E. (2006). "Ice: A strongly correlated proton system". Phys. Rev. B. 74 (2): 024302. arXiv: cond-mat/0511092 . Bibcode:2006PhRvB..74b4302C. doi:10.1103/PhysRevB.74.024302. S2CID 102581583.
- ↑ Drechsel-Grau, C.; Marx, D. (2014). "Quantum Simulation of Collective Proton Tunneling in Hexagonal Ice Crystals". Phys. Rev. Lett. 112 (14): 148302. Bibcode:2014PhRvL.112n8302D. doi:10.1103/PhysRevLett.112.148302. PMID 24766024.
- ↑ Yen, F.; Gao, T. (2015). "Dielectric Anomaly in Ice near 20 K: Evidence of Macroscopic Quantum Phenomena". J. Phys. Chem. Lett. 6 (14): 2822–2825. arXiv: 1508.00215 . doi:10.1021/acs.jpclett.5b00797. PMID 26266868. S2CID 38375110.
- ↑ Meng, X. Z.; et al. (2015). "Direct visualization of concerted proton tunnelling in a water nanocluster". Nat. Phys. 11 (3): 235–239. Bibcode:2015NatPh..11..235M. doi: 10.1038/NPHYS3225 .