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Water Dimer
The water dimer consists of two water (molecule), water molecules loosely bound by a hydrogen bond. It is the smallest water cluster. Because it is the simplest model system for studying hydrogen bonding in water, it has been the target of many theoretical (and later experimental) studies that it has been called a "theoretical Guinea pig". Structure and properties The Ab initio quantum chemistry methods, ab initio binding energy between the two water molecules is estimated to be 5-6 kcal/mol, although values between 3 and 8 have been obtained depending on the method. The experimentally measured dissociation energy (including nuclear quantum effects) of (H2O)2 and (D2O)2 are 3.16 ± 0.03 kcal/mol (13.22 ± 0.12 kJ/mol) and 3.56 ± 0.03 kcal/mol (14.88 ± 0.12 kJ/mol), respectively. The values are in excellent agreement with calculations. The O-O distance of the vibrational ground-state is experimentally measured at ca. 2.98 Å; the hydrogen bond is almost linear, but the angle wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Dimer
The water dimer consists of two water (molecule), water molecules loosely bound by a hydrogen bond. It is the smallest water cluster. Because it is the simplest model system for studying hydrogen bonding in water, it has been the target of many theoretical (and later experimental) studies that it has been called a "theoretical Guinea pig". Structure and properties The Ab initio quantum chemistry methods, ab initio binding energy between the two water molecules is estimated to be 5-6 kcal/mol, although values between 3 and 8 have been obtained depending on the method. The experimentally measured dissociation energy (including nuclear quantum effects) of (H2O)2 and (D2O)2 are 3.16 ± 0.03 kcal/mol (13.22 ± 0.12 kJ/mol) and 3.56 ± 0.03 kcal/mol (14.88 ± 0.12 kJ/mol), respectively. The values are in excellent agreement with calculations. The O-O distance of the vibrational ground-state is experimentally measured at ca. 2.98 Å; the hydrogen bond is almost linear, but the angle wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water (molecule)
Water () is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound and is described as the "universal solvent" and the "solvent of life". It is the most abundant substance on the surface of Earth and the only common substance to exist as a solid, liquid, and gas on Earth's surface. It is also the third most abundant molecule in the universe (behind molecular hydrogen and carbon monoxide). Water molecules form hydrogen bonds with each other and are strongly polar. This polarity allows it to dissociate ions in salts and bond to other polar substances such as alcohols and acids, thus dissolving them. Its hydrogen bonding causes its many unique properties, such as having a solid form less dense than its liquid form, a relatively high boiling point of 100 °C for its molar mass, and a high heat capacity. Water is amphoteric, mean ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Bond
In chemistry, a hydrogen bond (or H-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 , 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). Hydrogen bonds can be intermolecular (occurring between separate molecules) or intramolecular (occurring among parts of the same molecule). The energy of a hydrogen bond depends on the geometry, the environment, and the nature of the specific donor and acceptor atoms and can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, and weaker than fully covalent o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Cluster
In chemistry, a water cluster is a discrete hydrogen bonded assembly or cluster of molecules of water. Many such clusters have been predicted by theoretical models ( in silico), and some have been detected experimentally in various contexts such as ice, bulk liquid water, in the gas phase, in dilute mixtures with non-polar solvents, and as water of hydration in crystal lattices. The simplest example is the water dimer (H2O)2. Water clusters have been proposed as an explanation for some anomalous properties of liquid water, such as its unusual variation of density with temperature. Water clusters are also implicated in the stabilization of certain supramolecular structures. They are expected to play a role also in the hydration of molecules and ions dissolved in water. Theoretical predictions Detailed water models predict the occurrence of water clusters, as configurations of water molecules whose total energy is a local minimum. Of particular interest are the cyclic cluste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ab Initio Quantum Chemistry Methods
''Ab initio'' quantum chemistry methods are computational chemistry methods based on quantum chemistry. The term was first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene. The background is described by Parr. ''Ab initio'' means "from first principles" or "from the beginning", implying that the only inputs into an ''ab initio'' calculation are physical constants. ''Ab initio'' quantum chemistry methods attempt to solve the electronic Schrödinger equation given the positions of the nuclei and the number of electrons in order to yield useful information such as electron densities, energies and other properties of the system. The ability to run these calculations has enabled theoretical chemists to solve a range of problems and their importance is highlighted by the awarding of the Nobel prize to John Pople and Walter Kohn. Accuracy and scaling ''Ab initio'' electronic structure methods ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ad Van Der Avoird
Ad van der Avoird (born 19 April 1943) is a Dutch theoretical chemist. He is an emeritus professor of theoretical chemistry at the Radboud University Nijmegen. Education and career Van der Avoird was born on 19 April 1943 in Eindhoven. He studied at Eindhoven University of Technology, obtaining his PhD under George Schuit in 1968. In 1971, he joined the faculty of Radboud University Nijmegen and later became professor of theoretical chemistry. He took up emeritus status in 2008 although he kept working. In 2013 Van der Avoird provided a theory on the relation between two benzene rings and their possible motion, the discovery was published with Gerard Meijer and a German research team in a paper in ''Angewandte Chemie''. The model solved a decade old scientific issue. Honors and awards On 25 April 2014 he was made a Knight in the Order of the Netherlands Lion, one of only fifteen appointees that year. Amongst other accomplishments he was given the honor for his model of benzene d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Abstracts Service
CAS (formerly Chemical Abstracts Service) is a division of the American Chemical Society. It is a source of chemical information. CAS is located in Columbus, Ohio, United States. Print periodicals ''Chemical Abstracts'' is a periodical index that provides numerous tools such as SciFinder as well as tagged keywords, summaries, indexes of disclosures, and structures of compounds in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, available in at least 50 different languages, are monitored yearly, as are patent specifications from 27 countries and two international organizations. ''Chemical Abstracts'' ceased print publication on January 1, 2010. Databases The two principal databases that support the different products are CAplus and Registry. CAS References CAS References consists of bibliographic information and abstracts for all articles in chemical journals worldwide, and chemis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Forms Of Water
Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data *Form (education), a class, set, or group of students *Form (religion), an academic term for prescriptions or norms on religious practice *Form, a shallow depression or flattened nest of grass used by a hare *Form, or rap sheet, slang for a criminal record People * Andrew Form, American film producer * Fluent Form, Australian rapper and hip hop musician Arts, entertainment, and media * Form (visual art), a three-dimensional geometrical figure; one of the seven elements of art *Poetic form, a set of structural rules and patterns to which a poem may adhere *Musical form, a generic type of composition or the structure of a particular piece *The Forms (band), an American indie rock band Computing and technology *Form (computer virus), the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Chemistry
Water chemistry analyses are carried out to identify and quantify the chemical components and properties of water samples. The type and sensitivity of the analysis depends on the purpose of the analysis and the anticipated use of the water. Chemical water analysis is carried out on water used in industrial processes, on waste-water stream, on rivers and stream, on rainfall and on the sea. In all cases the results of the analysis provides information that can be used to make decisions or to provide re-assurance that conditions are as expected. The analytical parameters selected are chosen to be appropriate for the decision making process or to establish acceptable normality. Water chemistry analysis is often the groundwork of studies of water quality, pollution, hydrology and geothermal waters. Analytical methods routinely used can detect and measure all the natural elements and their inorganic compounds and a very wide range of organic chemical species using methods such as gas chr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cluster Chemistry
In chemistry, an atom cluster (or simply cluster) is an ensemble of bound atoms or molecules that is intermediate in size between a simple molecule and a nanoparticle; that is, up to a few nanometers (nm) in diameter. The term ''microcluster'' may be used for ensembles with up to couple dozen atoms. Clusters with a definite number and type of atoms in a specific arrangement are often considered a specific chemical compound and are studied as such. For example, fullerene is a cluster of 60 carbon atoms arranged as the vertices of a truncated icosahedron, and decaborane is a cluster of 10 boron atoms forming an incomplete icosahedron, surrounded by 14 hydrogen atoms. The term is most commonly used for ensembles consisting of several atoms of the same element, or of a few different elements, bonded in a three-dimensional arrangement. Transition metals and main group elements form especially robust clusters. Indeed, in some contexts, the term may refer specifically to a met ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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