Creation and recovery of a W(111) single atom gas field ion source

Tungsten single atom tips have been prepared from a single crystal W(111) oriented wire using the chemical assisted field evaporation and etching method. Etching to a single atom tip occurs through a symmetric structure and leads to a predictable last atom unlike etching with polycrystalline tips. The single atom tip formation procedure is shown in an atom by atom removal process. Rebuilds of single atom tips occur on the same crystalline axis as the original tip such that ion emission emanates along a fixed direction for all tip rebuilds. This preparation method could be utilized and developed to prepare single atom tips for ion source development.     

Remarks on the article by brandsma and arens: “di-(alkyne-1-yl)sulfides”

Summary When sulfur dichloride is added to 1-hexyne the sulfur atom attaches itself to the second carbon atom, and the chlorine atom to the first carbon atom.     

Is the dominance of even carbon atom molecules odd?

The unexpected higher frequency of occurrence of even carbon atom molecules over odd carbon atom ones revealed through previous database searches is shown to be a consequence of the predominantly bimolecular nature of bond formation processes and the fact that combinations of odd and odd as well as even and even atom molecules result in even atom products whereas odd and even atom molecule combinations alone lead to odd atom products.     

Application of atomic Hirshfeld surface analysis to intermetallic systems: is Mn in cubic CeMnNi4 a thermoelectric rattler atom?

The Mn atom in the cubic polymorph of CeMnNi(4) appears to be located in an oversized cage-like structure, and anomalously large atomic displacement parameters (ADPs) for the Mn atom indicate that it is a potential "rattler" atom. Here, multitemperature synchrotron powder X-ray diffraction data measured between 110 and 900 K are used to estimate ADPs for the Mn "guest" atom and the "host" structure atoms in cubic CeMnNi(4). The ADPs are subsequently fitted with Debye and Einstein models, giving Θ(D) = 301(2) K for the "host" structure and Θ(E) = 165(2) K for the Mn atom. This is higher than typical Einstein temperatures for rattlers in thermoelectric skutterudites and clathrates (Θ(E) = 50-80 K), indicating that the Mn atom in cubic CeMnNi(4) is more strongly bonded. In order to probe the chemical interactions of the potential Mn rattler atom, atomic Hirshfeld surface (AHS) analysis is carried out and compared with AHS analysis of well-established guest atom rattlers in archetypical skutterudites, MCoSb(3). Surprisingly, the skutterudite rattlers have more deformed AHSs than the Mn atom in cubic CeMnNi(4). This is related to the highly ionic nature of the skutterudite rattlers, which is not taken into account in the neutral spherical atom approach of the AHS. Additionally, visualization of void spaces in the two materials using the procrystal electron density shows that while the Mn atom is tightly fitting in the CeMnNi(4) structure then the La atom in the skutterudite is truly situated in an oversized cage of the host structure. Overall, we conclude that the Mn atom in cubic CeMnNi(4) cannot be coined a rattler.     

Unusual mechanisms can dominate reactions at hyperthermal energies: an example from O(3P) + HCl --> ClO + H

An unusual mechanism in the reaction, O(3P) + HCl --> ClO + H, dominates at hyperthermal collision energies. This mechanism applies to collision geometries in which the H atom in the HCl molecule is oriented toward the reagent O atom. As the Cl-O bond forms, the H atom experiences a strong repulsive force from both the O and Cl atoms. The ClO product scatters forward with respect to the initial velocity of the O atom, and the H atom scatters backward. This mechanism accounts for more than half the reactive trajectories at energies >110 kcal mol-1, but it does not involve motion near the minimum energy path, which favors an SN2-like reaction mechanism where the H atom is oriented away from the reagent O atom during the collision.     

异丙基膦酸单烷基酯萃取剂的量子化学研究

用分子力学、分子动力学及半经验量子化学方法研究了异丙基膦酸单烷基酯系列稀土萃取剂的空间结构和电子结构、结果表明，烷氧基上的取代基对空间位阻的影响比主碳链大。与稀土原子配位的磷酰氧原子在ＨＯＭＯ中的贡献较大，而ＬＵＭＯ轨道则主要由非配位原子的轨道组成。萃取剂中磷原子、磷酰氧原子以及羟基中氧原子上的电荷分布均随结构的变化呈规律性变化。磷原子和磷酰氧原子上的电荷分布与萃取剂的ｐＫａ值呈线性关系。     

Association of Haloforms in Condensed and Gas Phases. Ir Spectroscopy and Dft Calculations

Fourier-transform infrared (FTIR) spectra are recorded for the haloforms of fluorine, chlorine, and bromine atoms in gas and liquid phases, as well as for their low-temperature films at 20–200 K. The molecules of these compounds are shown to be connected by hydrogen bonds associated with the transfer of a hydrogen atom. According to ab initio DFT calculations, chloroform demonstrates two types of associated structures, one with the chlorine atom and the other with the central carbon atom binding as the proton acceptor in the intermolecular interaction. At the same time, calculations predict only one form of bonding for two other haloforms, namely, between the hydrogen atom and the fluorine atom for fluoroform, and between the hydrogen atom and the carbon atom for bromoform.     

INDO study of 1,2-fluorine atom migration in 1,2-difluoroethyl and 1,1,2-trifluoroethyl radicals

INDO molecular orbital calculations have been carried out to estimate the barrier heights to the 1,2-migration of fluorine and hydrogen atoms in 1,2-difluoroethyl and 1,1,2-trifluoroethyl radicals. The calculated results suggest that (1) the 1,2-fluorine atom migration through a fluorine atom bridging intermediate will occur more readily than the 1,2-hydrogen atom migration through a hydrogen atom bridging intermediate in both radicals, (2) a fluorine atom will undergo 1,2-migration in 1,1,2-trifluoroethyl radical more readily than in 1,2-difluoroethyl radical. The enthalpy change accompanied by the 1,2-fluorine atom migration in 1,1,2-trifluoroethyl radical was estimated to be 1.7 kcal/mol, which was in good agreement with the value(1.6 kcal/mol) obtained experimentally.     

黄酮类化合物中不同化学态氧的XPS分析

利用ＸＰＳ测定了黄酮类化合物中苯氧原子、酚氧原子、醇氧原子、醚氧原子以及羰基氧原子Ｏｌｓ的结合能,它们分别为５３３．８５ｅＶ、５３３．１０ｅＶ、５３２．５５ｅＶ、５３２．１５ｅＶ和５３１．２５ｅＶ。     

Real-time study of the adiabatic energy loss in an atomic collision with a metal cluster

Gas-phase hydrogen atoms are accelerated towards metallic surfaces in their vicinity. As it approaches the surface, the velocity of an atom increases and this motion excites the metallic electrons, causing energy loss to the atom. This dissipative dynamics is frequently described as atomic motion under friction, where the friction coefficient is obtained from ab initio calculations assuming a weak interaction and slow atom. This paper tests the aforementioned approach by comparing to a real-time Ehrenfest molecular dynamics simulation of such a process. The electrons are treated realistically using standard approximations to time-dependent density functional theory. We find indeed that the electronic excitations produce a friction-like force on the atom. However, the friction coefficient strongly depends on the direction of the motion of the atom: it is large when the atom is moving towards the cluster and much smaller when the atom is moving away. It is concluded that a revision of the model for energy dissipation at metallic surfaces, at least for clusters, may be necessary.     

Stereo- and Site-Selectivity in the Reaction of Chiral Episelenonium Ion with Carbon Nucleophile

Abstract

There are two important aspects in the reaction of chiral episelenonium ion (episelenonium ion bearing chiral carbon in the three-membered ring) with carbon nucleophile; namely, (1) whether the chiral carbon racemizes during the reaction or not, and (2) the carbon nucleophile attacks the carbon atom (carbophilic attack) or selenium atom (selenophilic attack) in the three-membered ring. When carbon nucleophile such as alkenyl silyl ethers, trimethylsilyl cyanide, and allyltrimethyl-silane are employed, steric protection of the selenium atom by the attachment of tri-tert-butylphenyl (TTBP) group to the selenium atom is inevitable to avoid both of the racemization of the chiral carbon atom and selenophilic attack of the carbon nucleophile. When aromatic compounds are employed as carbon nucleophile, on the other hand, selenophilic attack is rarely observed irrespective of the nature of the aryl group on the selenium atom and introduction of electron withdrawing group into the aryl group on the selenium atom is effective to retard the racemization of the chiral carbon atom.     

Neutron crystallographic and molecular dynamics studies of the structure of ammonia-cellulose I: rearrangement of hydrogen bonding during the treatment of cellulose with ammonia

The hydrogen bond arrangement in a complex of cellulose with ammonia has been studied using neutron crystallography in combination with molecular dynamics simulations. The O6 atom of the hydroxymethyl group is donor in a highly occupied hydrogen bond to an ammonia molecule. This rotating ammonia molecule is donor in partially occupied and transient hydrogen bonds to the O2, O3 and O6 atoms of the hydroxyl groups of other chains. The hydrogen atom bound to the O3 atom is disordered but it is almost always involved in some type of hydrogen bonding. It is donated in a hydrogen bond most of the time to the O5 atom on the same chain. However, it also rotates away from this O5 atom to be donated to an ammonia molecule part of the time. On the other hand the hydrogen atom bound to the O2 atom is free from hydrogen bonding most of the time. It is donated in a hydrogen bond to the O6 atom on a neighboring chain only with a relatively small probability. These results provide new insights into how hydrogen bonds are rearranged during the conversion of cellulose I to cellulose III_I by ammonia treatment.     

Reaction of dichlorophosphorylimidophosphorus trichloride with nucleophilic reagents

Conclusions When dichlorophosphorylimidophosphorus trichloride is reacted with nucleophilic reagents (phenols, dialkylamines, and their trimethylsilyl derivatives), the first to be replaced is the chloride atom on the imido P atom. As the result of further reaction with phenol the substitution at the imido P atom continues, while when reaction is with diethylamine or diethylaminotrimethylsilane the chlorine atom on the phosphoryl P atom is replaced.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2379–2386, October, 1980.     

取代基咪唑啉与铁原子化学吸附作用能的量子化学计算

用量子化学方法计算了６个咪唑啉型化合物及其与铁原子的化学吸附作用能,探讨了这种作用能与缓蚀性能的关系。得到咪唑啉环上氮与铁的配位键长、双原子作用能以及重叠集居数。研究发现具有ｐ－π共轭体系的咪唑啉以及在环上引入供电子基团或取代芳烃,能增强氮与铁原子的化学吸附作用力。计算结果可为设计性能较好的新型咪唑啉缓蚀剂提供有用的信息。     

Electronic structure of organylthiochloroacetylenes and their reactions with O-containing nucleophiles

Conclusions Reactivity of organylthiochloroacetylenes toward O-containing nucleophiles was studied. It was established that phenolate anions attack the acetylenic C atom bound to the Cl atom and alcoholate anions attack the carbon atom bound to the S atom, which corresponds with the data of quantum chemical calculations.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya No. 3, pp. 612–616, March, 1988.     

International Review of Science Solid State Chemistry,Inorganic Chemistry Series Two,Vol. 10 : Consultant Editor H.J. Emeleus FRS,Volume Editor L.E.J. Roberts,Butterworths, London, 1975, pp. 264, price £13.00

Complexes of nicotinic and isonicotinic acids and their deuterated analogues with pyridine, 4-Me pyridine and N Me imidazole have been examined by IR spectroscopy. Strong hydrogen bonding between an O atom of the acid and the N atom of the base with the H atom lying closer to the O atom, is present in all systems.     

Spatial and electronic structure and 35Cl NQR parameters of ethyl(trichlorogermyl) propionate according to Ab initio calculations

Two stable structures of ethyl(trichlorogermyl) propionate have been studied by RHF/6-31G(d) and MP2/6-31G(d) quantum-chemical caclulation with full geometry optimization. The structure with pentacoordinated Ge atom has been more stable than that with tetracoordinated Ge atom. Based on the computation results, the frequencies of ³⁵Cl nuclear quadrupole resonance of the studied compound with pentacoordinated Ge atom has been estimated, it has been in satisfactory agreement with the experimental data. Additionally, the calculations by means of the RHF/6-31G(d) method have been performed at various fixed Ge…O interatomic distances. When the Ge and O coordination centers get closer, both the positive charge on Ge and the negative charge on O increase. The electron density shifts from Ge atom to the axial Cl atom, and the electron density shifst from the carbonyl C atom to the carbonyl oxygen atom. The electron density charge trasfer from O to Ge does not occur.     

Cyclocondensation of Ethyl (imidazolidine‐2‐ylidene)acetate with Aromatic Esters Bearing Labile Halogen in ortho‐Position

Cyclocondensation of ethyl (imidazolidine‐2‐ylidene)acetate with aromatic esters bearing labile halogen in ortho‐position leads to fused heterocycles, which is formed by substitution of halogen atom with α‐carbon atom of cyclic ketene aminal and binding of nitrogen atom with carbonyl carbon atom of aromatic ester.     

Regulating Charge Transfer of Lattice Oxygen in Single‐Atom‐Doped Titania for Hydrogen Evolution

Single‐atom catalysts have attracted much attention. Reported herein is that regulating charge transfer of lattice oxygen atoms in serial single‐atom‐doped titania enables tunable hydrogen evolution reaction (HER) activity. First‐principles calculations disclose that the activity of lattice oxygen for the HER can be regularly promoted by substituting its nearest metal atom, and doping‐induced charge transfer plays an essential role. Besides, the realm of the charge transfer of the active site can be enlarged to the second nearest atom by creating oxygen vacancies, resulting in further optimization for the HER. Various single‐atom‐doped titania nanosheets were fabricated to validate the proposed model. Taking advantage of the localized charge transfer to the lattice atom is demonstrated to be feasible for realizing precise regulation of the electronic structures and thus catalytic activity of the nanosheets.     

Long-range energy transfer and ionization in extended quantum systems driven by ultrashort spatially shaped laser pulses

The processes of ionization and energy transfer in a quantum system composed of two distant H atoms with an initial internuclear separation of 100 atomic units (5.29 nm) have been studied by the numerical solution of the time-dependent Schr?dinger equation beyond the Born-Oppenheimer approximation. Thereby it has been assumed that only one of the two H atoms was excited by temporally and spatially shaped laser pulses at various laser carrier frequencies. The quantum dynamics of the extended H-H system, which was taken to be initially either in an unentangled or an entangled ground state, has been explored within a linear three-dimensional model, including the two z coordinates of the electrons and the internuclear distance R. An efficient energy transfer from the laser-excited H atom (atom A) to the other H atom (atom B) and the ionization of the latter have been found. It has been shown that the physical mechanisms of the energy transfer as well as of the ionization of atom B are the Coulomb attraction of the laser driven electron of atom A by the proton of atom B and a short-range Coulomb repulsion of the two electrons when their wave functions strongly overlap in the domain of atom B.