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A phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids.A type of quasiparticle in physics, [1] a phonon is an excited state in the quantum mechanical quantization of the modes of vibrations for elastic structures of interacting particles.
The spectrum of densities is wide-ranging: from 10 15 g/cm 3 for neutron stars, 1.00 g/cm 3 for water, to 1.2×10 −3 g/cm 3 for air. [13] Other relevant parameters are area density which is mass over a (two-dimensional) area, linear density - mass over a one-dimensional line, and relative density , which is a density divided by the density of ...
The term "chiral" in general is used to describe the object that is non-superposable on its mirror image. [18] In chemistry, chirality usually refers to molecules. Two mirror images of a chiral molecule are called enantiomers or optical isomers. Pairs of enantiomers are often designated as "right-", "left-handed" or, if they have no bias ...
A chiral phenomenon is one that is not identical to its mirror image (see the article on mathematical chirality). The spin of a particle may be used to define a handedness, or helicity, for that particle, which, in the case of a massless particle, is the same as chirality. A symmetry transformation between the two is called parity transformation.
Two enantiomers of a generic amino acid that are chiral (S)-Alanine (left) and (R)-alanine (right) in zwitterionic form at neutral pH. In chemistry, a molecule or ion is called chiral (/ ˈ k aɪ r əl /) if it cannot be superposed on its mirror image by any combination of rotations, translations, and some conformational changes.
Phonons take on both labels such that transverse acoustic and optical phonons are denoted TA and TO, respectively; likewise, longitudinal acoustic and optical phonons are denoted LA and LO. The type of surface phonon can be characterized by its dispersion in relation to the bulk phonon modes of the crystal.
Chirality in supramolecular chemistry implies the non-symmetric arrangement of molecular components in a non-covalent assembly. Chirality may arise in a supramolecular system if one of its component is chiral or if achiral components arrange in a non symmetrical way to produce a supermolecule that is chiral. [1]
A planar chiral derivative of ferrocene, used for kinetic resolution of some racemic secondary alcohols [1]. This term is used in chemistry contexts, [2] e.g., for a chiral molecule lacking an asymmetric carbon atom, but possessing two non-coplanar rings that are each dissymmetric and which cannot easily rotate about the chemical bond connecting them: 2,2'-dimethylbiphenyl is perhaps the ...