|
Rotational–vibrational Spectroscopy
Rotational–vibrational spectroscopy is a branch of molecular spectroscopy concerned with infrared and Raman spectra of molecules in the gas phase. Transitions involving changes in both vibrational and rotational states can be abbreviated as rovibrational (or ro-vibrational) transitions. When such transitions emit or absorb photons (electromagnetic radiation), the frequency is proportional to the difference in energy levels and can be detected by certain kinds of spectroscopy. Since changes in rotational energy levels are typically much smaller than changes in vibrational energy levels, changes in rotational state are said to give fine structure to the vibrational spectrum. For a given vibrational transition, the same theoretical treatment as for pure rotational spectroscopy gives the rotational quantum numbers, energy levels, and selection rules. In linear and spherical top molecules, rotational lines are found as simple progressions at both higher and lower frequencies relat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter waves and acoustic waves can also be considered forms of radiative energy, and recently gravitational waves have been associated with a spectral signature in the context of the Laser Interferometer Gravitational-Wave Observatory (LIGO) In simpler terms, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Historically, spectroscopy originated as the study of the wavelength dependence of the absorption by gas phase matter of visible light dispersed by a prism. Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of astronomy, chemistry, materials science, and physics, allowing the composition, physical structure and e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wavenumbers
In the physical sciences, the wavenumber (also wave number or repetency) is the ''spatial frequency'' of a wave, measured in cycles per unit distance (ordinary wavenumber) or radians per unit distance (angular wavenumber). It is analogous to temporal frequency, which is defined as the number of wave cycles per unit time (''ordinary frequency'') or radians per unit time (''angular frequency''). In multidimensional systems, the wavenumber is the magnitude of the ''wave vector''. The space of wave vectors is called ''reciprocal space''. Wave numbers and wave vectors play an essential role in optics and the physics of wave scattering, such as X-ray diffraction, neutron diffraction, electron diffraction, and elementary particle physics. For quantum mechanical waves, the wavenumber multiplied by the reduced Planck's constant is the ''canonical momentum''. Wavenumber can be used to specify quantities other than spatial frequency. For example, in optical spectroscopy, it is often use ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simplest molecule of the oxocarbon family. In coordination complexes the carbon monoxide ligand is called carbonyl. It is a key ingredient in many processes in industrial chemistry. The most common source of carbon monoxide is the partial combustion of carbon-containing compounds, when insufficient oxygen or heat is present to produce carbon dioxide. There are also numerous environmental and biological sources that generate and emit a significant amount of carbon monoxide. It is important in the production of many compounds, including drugs, fragrances, and fuels. Upon emission into the atmosphere, carbon monoxide affects several processes that contribute to climate change. Carbon monoxide has important biological roles across phylogenetic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NO R-branch
No (and variant writings) may refer to one of these articles: English language * ''Yes'' and ''no'' (responses) * A determiner in noun phrases Alphanumeric symbols * No (kana), a letter/syllable in Japanese script * No symbol, displayed 🚫 * Numero sign, a typographic symbol for the word 'number', also represented as "No." or similar variants Geography * Norway (ISO 3166-1 country code NO) ** Norwegian language (ISO 639-1 code "no"), a North Germanic language that is also the official language of Norway ** .no, the internet ccTLD for Norway * Lake No, in South Sudan * No, Denmark, village in Denmark * Nō, Niigata, a former town in Japan * No Creek (other) * Acronym for the U.S. city of New Orleans, Louisiana or its professional sports teams ** New Orleans Saints of the National Football League ** New Orleans Pelicans of the National Basketball Association Arts and entertainment Film and television * ''Dr. No'' (film), a 1962 ''James Bond'' film ** Juli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dunham Expansion
In quantum chemistry, the Dunham expansion is an expression for the rotational-vibrational energy levels of a diatomic molecule: : E(v,J,\Omega) = \sum_ Y_ (v+1/2)^k (J+1) - \Omega^2l, where v and J are the vibrational and rotational quantum numbers, and \Omega is the projection of J along the internuclear axis in the body-fixed frame. The constant coefficients Y_ are called Dunham parameters with Y_ representing the electronic energy. The expression derives from a semiclassical treatment of a perturbational approach to deriving the energy levels. The Dunham parameters are typically calculated by a least-squares The method of least squares is a standard approach in regression analysis to approximate the solution of overdetermined systems (sets of equations in which there are more equations than unknowns) by minimizing the sum of the squares of the res ... fitting procedure of energy levels with the quantum numbers. Relation to conventional band spectrum constants Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Born–Oppenheimer Approximation
In quantum chemistry and molecular physics, the Born–Oppenheimer (BO) approximation is the best-known mathematical approximation in molecular dynamics. Specifically, it is the assumption that the wave functions of atomic nuclei and electrons in a molecule can be treated separately, based on the fact that the nuclei are much heavier than the electrons. Due to the larger relative mass of a nucleus compared to an electron, the coordinates of the nuclei in a system are approximated as fixed, while the coordinates of the electrons are dynamic. The approach is named after Max Born and J. Robert Oppenheimer who proposed it in 1927, in the early period of quantum mechanics. The approximation is widely used in quantum chemistry to speed up the computation of molecular wavefunctions and other properties for large molecules. There are cases where the assumption of separable motion no longer holds, which make the approximation lose validity (it is said to "break down"), but even then t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centre Of Mass
In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may be applied to cause a linear acceleration without an angular acceleration. Calculations in mechanics are often simplified when formulated with respect to the center of mass. It is a hypothetical point where the entire mass of an object may be assumed to be concentrated to visualise its motion. In other words, the center of mass is the particle equivalent of a given object for application of Newton's laws of motion. In the case of a single rigid body, the center of mass is fixed in relation to the body, and if the body has uniform density, it will be located at the centroid. The center of mass may be located outside the physical body, as is sometimes the case for hollow or open-shaped objects, such as a horseshoe. In the case of a distri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anharmonicity
In classical mechanics, anharmonicity is the deviation of a system from being a harmonic oscillator. An oscillator that is not oscillating in harmonic motion is known as an anharmonic oscillator where the system can be approximated to a harmonic oscillator and the anharmonicity can be calculated using perturbation theory. If the anharmonicity is large, then other numerical techniques have to be used. In reality all oscillating systems are anharmonic, but most approximate the harmonic oscillator the smaller the amplitude of the oscillation is. As a result, oscillations with frequencies 2\omega and 3\omega etc., where \omega is the fundamental frequency of the oscillator, appear. Furthermore, the frequency \omega deviates from the frequency \omega_0 of the harmonic oscillations. See also intermodulation and combination tones. As a first approximation, the frequency shift \Delta \omega=\omega-\omega_0 is proportional to the square of the oscillation amplitude A: :\Delta \omeg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Appendix '', a quarterly journal of history and culture
{{disambiguation ...
Appendix, or its plural form appendices, may refer to: __NOTOC__ In documents * Addendum, an addition made to a document by its author after its initial printing or publication * Bibliography, a systematic list of books and other works * Index (publishing), a list of words or phrases with pointers to where related material can be found in a document Anatomy * Appendix (anatomy), a part of the human digestive system Arts and media * Appendix (band), a Finnish punk rock group * ''The Appendix ''The Appendix'' was an online magazine of "narrative and experimental history." It was co-founded in the fall of 2012 by Benjamin Breen, Felipe Cruz, Christopher Heaney, and Brian Jones. A stated goal of the journal is that "scholarly and popul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Least-squares
The method of least squares is a standard approach in regression analysis to approximate the solution of overdetermined systems (sets of equations in which there are more equations than unknowns) by minimizing the sum of the squares of the residuals (a residual being the difference between an observed value and the fitted value provided by a model) made in the results of each individual equation. The most important application is in data fitting. When the problem has substantial uncertainties in the independent variable (the ''x'' variable), then simple regression and least-squares methods have problems; in such cases, the methodology required for fitting errors-in-variables models may be considered instead of that for least squares. Least squares problems fall into two categories: linear or ordinary least squares and nonlinear least squares, depending on whether or not the residuals are linear in all unknowns. The linear least-squares problem occurs in statistical regression ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
