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PubMed Journals Articles About "Determination Interval Between Ground States Para Ortho" RSS

11:45 EST 10th December 2019 | BioPortfolio

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Showing "Determination Interval between Ground States Para Ortho" PubMed Articles 1–25 of 10,000+

Determination of the Interval between the Ground States of Para- and Ortho-H_{2}.

Nuclear-spin-symmetry conservation makes the observation of transitions between quantum states of ortho- and para-H_{2} extremely challenging. Consequently, the energy-level structure of H_{2} derived from experiment consists of two disjoint sets of level energies, one for para-H_{2} and the other for ortho-H_{2}. We use a new measurement of the ionization energy of para-H_{2} [E_{I}(H_{2})/(hc)=124 417.491 098(31)  cm^{-1}] to determine the energy separation [118.486 770(50)  cm^{-1}] between...


Collisional Excitation of CF by H: Potential Energy Surface and Rotational Cross Sections.

The CF+ molecule is considered as one of the key species for the study of fluorine chemistry in the interstellar medium (ISM). Its recent detection, as well as its potential use as a tracer for atomic fluorine in the ISM, have increased the interest in the study of the physical and chemical properties of this cation. Accurate determination of the CF+ abundance in the ISM requires detailed modeling of its excitation from both radiation and collisions with the most dominant species, which are usually atomic a...

Simplified Treatment of Electronic Structures of the Lowest Singlet and Triplet States of Didehydropyrazines.

Experiments on the lowest lying singlet and triplet states of didehydropyrazine isomers (that focus on energy gaps, geometries, and vibrational frequencies) have been carried out computationally by implementing the improved virtual orbital-based multireference (MR) ab initio methods. Pyrazines possess a reasonable MR nature making their description challenging with the conventional quantum chemical approaches. Although wave functions of the diradicals usually have two dominant configurations, a larger refer...


Theoretical Explanation of Reaction Site Selectivity in the Addition of a Phenoxy Group to Perfluoropyridine.

Pentafluoropyridine, a potentially useful precursor in organofluorine methodology, undergoes selective substitution of a fluorine with a phenoxide at the site para to the nitrogen. Subsequent aryloxide substitutions can be accomplished at the ortho positions with aryloxide groups containing various functional groups para to the phenoxide oxygen. During this phase of the reaction, "reverse reactions" involving substitutions of the original para substituent with a free fluoride or with another aryloxide moiet...

Effects of aquaculture effluents on fate of 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) in contaminated mangrove sediment planted with Kandelia obovata.

The problems of aquaculture effluent (AE) and polybrominated diphenyl ethers (PBDEs) are common in coastal areas. The fate of 2,2',4,4',5-pentabromodiphenyl ether (BDE-99), a dominant PBDE congener, in mangrove sediments and the effects of AE on it have never been reported. A 12-months microcosm study was conducted and more than 55% of the BDE-99 in contaminated sediment was removed at the end. The removal percentages depended on treatments, with the highest removal in the treatment planted with Kandelia ob...

Quantum State-Resolved Characterisation of a Magnetically-Focused Beam of Ortho-HO.

Magnetic focusing of a molecular beam formed from a rotationally-cooled supersonic jet of HO seeded in argon is shown to yield water vapour highly enriched in the ortho-HO nuclear spin isomer (NSI). Rotationally-resolved resonance-enhanced multi-photon ionisation time-of-flight mass spectrometry demonstrates that this methodology enables the preparation of a beam of water molecules enriched to >98 % in the ortho-HO NSI, that is having an ortho-to-para ratio (OPR) in excess of 50:1. The flux and quantum-stat...

Structural isomers of cinnamic hydroxamic acids block HCV replication via different mechanisms.

A set of ortho-, meta- and para-substituted cinnamic hydroxamic acids (CHAs) was synthesized. In each series of structural isomers, a phenyl substituent was linked to an aromatic ring of the parent cinnamic acid via a linker of one to four atoms in length. Using a cell test system with the full-length replicon of hepatitis C virus (HCV), we established a relationship between the suppression of HCV replicon propagation and the inhibition of class I/IIb histone deacetylases (HDACs). Anti-HCV activity correlat...

A General Approach for Multireference Ground and Excited States using Non-Orthogonal Configuration Interaction.

A balanced description of ground and excited states is essential for the description of many chemical processes. However, few methods can handle cases where static correlation is present, and often these scale very unfavourably with system size. Recently, multiple Hartree--Fock (HF) solutions have been proposed as a basis for non-orthogonal configuration interaction (NOCI) to provide multireference ground and excited state energies, although applications across multiple geometries have been limited by the c...

Stand Your Ground: Policy and Trends in Firearm-Related Justifiable Homicide and Homicide in the US.

In recent years, several states have enacted Stand Your Ground (SYG) legislation intended to deter crime. To date, the impact of these laws on justifiable homicide (JH) and homicide (HOM) is unknown. This study was designed to compare JH and HOM rates (JHR, HR) before and after enactment of SYG laws and in states with and without (NoSYG) such legislation.

Photochemical Amplifier Based on Self-Immolative Dendritic Spacers.

A self-immolative dendritic structure was synthesized. It is based on phenol derivatives with three hydroxymethyl arms at both ortho and para positions of the core unit, potentially releasing up to 27 leaving groups in a third-generation dendrimer. The triggering event is the photolysis of a photosentive ortho-nitrobenzyl group. In doing so, we expected to transform a weak chemical or photochemical input into a large chemical output, which fulfills the definition of a molecular amplifier. Such dendrimers co...

An Improved Ion Chromatographic Method for Fast and Sensitive Determination of Hexavalent Chromium and Total Chromium Using Conductivity Detection.

Chromium exists in its two stable oxidation states including trivalent chromium (Cr (III)) and hexavalent chromium (Cr (VI)) in natural waters. Chromium is an essential micronutrient in the trivalent form; however, the hexavalent form of chromium is considered to be a carcinogen. It is important to determine the chromium content along with speciation. There are a number of methods available for chromium determination. Speciation of chromium is essential to know the exact composition of chromium. Ion exchang...

Dearomatization of Electron-Deficient Phenols to ortho-Quinones Enabled by Bidentate Nitrogen-Ligated I(V) Reagents.

Ortho-quinones are versatile functional groups found in nature, materials science, and total synthesis. Despite their broad utility, the synthesis of o-quinones remains a significant challenge, and in particular, access to electron-deficient derivatives remains an unsolved problem. Herein, we report the first general method for the synthesis of electron-deficient o-quinones via the direct oxidation of phenols. The reaction is enabled by a novel bidentate nitrogen-ligated I(V) reagent, a previously unexplore...

Influence of the degree of oligomerization of surfactants on the DNA/surfactant interaction.

The interaction between calf thymus DNA, ctDNA, and a series of oligomeric surfactants derived from N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium chloride is investigated. The influence of the surfactants' degree of oligomerization (2, 3 and 4) on the ctDNA/surfactant interaction is studied, as well as the effect of the structure of the spacer group linking the individual surfactant fragments. In particular, the effect of the distance between the positive charges and the hydrophobic chains within the oligomer...

pH-Induced Binding of the Axial Ligand in an Engineered Cu Site Favors the π State.

Cu centers perform efficient long-range electron transfer. The electronic structure of native Cu sites can be described by a double-potential well with a dominant σ* ground state in fast equilibrium with a less populated π ground state. Here, we report a Cu mutant in which a lysine was introduced in the axial position. This results in a highly unstable protein with a pH-dependent population of the two ground states. Deep analysis of the high-pH form of this variant shows the stabilization of the π ground...

Exchange rules for diradical π-conjugated hydrocarbons.

A variety of planar π-conjugated hydrocarbons such as heptauthrene, Clar's goblet and, recently synthesized, triangulene have two electrons occupying two degenerate molecular orbitals. The resulting spin of the interacting ground state is often correctly anticipated as S = 1, extending the application of Hund's rules to these systems, but this is not correct in some instances. Here we provide a set of rules to correctly predict the existence of zero mode states, as well as the spin multiplicity of both the...

Dyson orbitals within the fc-CVS-EOM-CCSD framework: theory and application to X-ray photoelectron spectroscopy of ground and excited states.

We report on the implementation of Dyson orbitals within the recently introduced frozen-core (fc) core-valence separated (CVS) equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method, which enables efficient and reliable characterization of core-level states. The ionization potential (IP) variant of fc-CVS-EOM-CCSD, in which the EOM target states have one electron less than the reference, gives access to core-ionized states thus enabling modeling of X-ray photoelectron spectra (XPS) and i...

Halide Perovskite-Derived Compounds RbTeX (X = Cl, Br, and I): Electronic Structure of the Ground and First Excited States.

Herein, we report a study of the electronic structure of the ground and first excited states of RbTeCl, RbTeBr, and RbTeI halide-perovskite-derived crystals. Using X-ray photoelectron spectroscopy (XPS) measurements and density functional theory and multiconfiguration self-consistent field (MCSCF) calculations, the experimental and theoretical XPS spectra of the valence region were obtained. In addition, the effects of the cations and halogen atoms on the electronic structure were determined, and the classi...

Excited States in Bilayer Graphene Quantum Dots.

We report ground- and excited-state transport through an electrostatically defined few-hole quantum dot in bilayer graphene in both parallel and perpendicular applied magnetic fields. A remarkably clear level scheme for the two-particle spectra is found by analyzing finite bias spectroscopy data within a two-particle model including spin and valley degrees of freedom. We identify the two-hole ground state to be a spin-triplet and valley-singlet state. This spin alignment can be seen as Hund's rule for a val...

Regioselective oxidative arylation of fluorophenols.

A metal free and highly regioselective oxidative arylation reaction of fluorophenols is described. The relative position of the fluoride leaving group (ie ortho or para ) controls the 1,2 or 1,4 nature of the arylated quinone product, lending versatility and generality to this oxidative, defluorinative, arylation concept.

The Electron Localization Function in Excited States: The case of the ultra-fast proton transfer of the salicylidene methylamine.

The physical characterization of the chemical bond in the ground state has been a central theme to theoretical chemistry. Among many techniques, quantum chemical topology (QCT) has emerged as a robust technique to understand the features of the chemical bond and electron organization within molecules. One consolidate tool within QCT is the topological analysis of the electron localization function (ELF). Most research on ELF and chemical bond has focused either on singlet ground states or the first excited ...

State variation in early-onset colorectal cancer in the United States, 1995-2015.

The extent to which the increase in early-onset colorectal cancer (CRC) in the US varies geographically is unknown. We analyzed changes in CRC incidence and risk factors among people 20-49 years by state using high-quality population-based cancer registry data provided by the North American Association of Central Cancer Registries and national survey data, respectively. Early-onset CRC incidence was mostly stable among blacks and Hispanics, but increased in 40/47 states among non-Hispanic-whites, most promi...

Regioselective Ortho Amination of an Aromatic C-H Bond by Trifluoroacetic Acid via Electrochemistry.

A trifluoroacetic acid-facilitated ortho amination of alkoxyl arene has been established via anodic oxidation in an undivided cell. In the absence of any additional metal or oxidant reagents, a series of aromatic and heteroaromatic amine derivatives have been synthesized in good to excellent yields. Our findings reveal the possibility of achieving complete ortho-selective amination of a simple arene, which emerges as an efficient route for facile and large-scale organic synthesis.

Gold with +4 oxidation state compounds: mass spectrometric and theoretical characterization of AuO.

Using an ab initio methodology and mass spectrometric study we identify AuO2+ as a metastable species in the gas phase. This represents the first characterization of a gas phase compound of gold with the oxidation state +4. Computations show that this dication exhibits deep potential wells with long lived electronic states. Its electronic ground state is of 4∑- symmetry, which is known for very few molecular ground states. We also discussed the O + Au2+ collision dynamics, which leads mostly to charge tra...

A model for the peak-interval task based on neural oscillation-delimited states.

Specific mechanisms underlying how the brain keeps track of time are largely unknown. Several existing computational models of timing reproduce behavioral results obtained with experimental psychophysical tasks, but only a few tackle the underlying biological mechanisms, such as the synchronized neural activity that occurs throughout brain areas. In this paper, we introduce a model for the peak-interval task based on neuronal network properties. We consider that Local Field Potential (LFP) oscillation cycle...

From phenols to quinones: Thermodynamics of radical scavenging activity of para-substituted phenols.

Radical scavenging activity and subsequent oxidation resulting in quinone products represent one of the important features of phenols occurring in plants and other biological systems. However, corresponding thermochemistry data can be still considered scarce. For phenol and 25 para-substituted phenols, we investigate the thermodynamics of the individual reaction steps, including three subsequent hydrogen atom transfers, as well as hydroxyl HO radical addition, leading to final ortho-quinone formation. The s...


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