Reactions of Atoms

Several methods for the quantitative investigation of reactions of free atoms in the gas phase have been developed in recent years. The present article deals with reactions of hydrogen, carbon, oxygen, and halogen atoms with simple molecules. The results of such investigations are of fundamental importance for the understanding of chemical reactions and for many technical applications, such as explosion and combustion processes, halogenations, and chemical lasers.     

Look Better: Single Atoms in Chemistry and Single Atoms in Physics

Fostering fruitful collaboration between chemistry and physics scholars, the analysis of the differences in the practical approach to single atoms in chemistry and in physics affords a number of conceptual outcomes pointing to a more balanced and useful relationship between chemistry and physics.     

Noncovalent Bonds between Tetrel Atoms

The pairing of TFH₃ with a TH₂CH₃⁻ anion, where T represents tetrel atoms C, Si, Ge, Sn, Pb, results in a strong direct interaction between the two T atoms. The interaction energy is sensitive to the nature of the two T atoms but can be as large as 90 kcal/mol. The noncovalent bond strength rises quickly as the basic T atom of the anion becomes smaller, or as the Lewis acid T grows larger, although there is less sensitivity to the latter atom. The electrostatic component makes up some 55–70 % of the total attraction energy. This term is well accounted for by simple combination of the maximum and minimum values of the molecular electrostatic potential of the Lewis acid and base units, respectively. The complexation induces a rearrangement in the TFH₃ molecule from tetrahedral to trigonal pyramidal. The associated deformation energy reduces the exothermicity of the complexation reaction. Electron density shift patterns reveal a density loss on the basic T atom, along with accompanying increases on the acidic T and its attached F atom.     

多电子原子的结构

论述了不同精度Hamilton算符下多电子原子的结构,并对Slater行列式、电子组态、原子光谱项和光谱支项等相关内容进行了讨论。     

高压下的原子和分子行为

近些年,高压化学的研究取得了非常多的成果。本文从基础化学原理出发,讨论高压对原子轨道能量和化学键的影响。高压下,原子轨道能量会发生改变,从而导致核外电子在轨道间的重新排布,影响到元素的化学性质。于分子而言,高压下分子晶体会发生相变,不饱和化合物会发生自聚,饱和化合物则有可能金属化。     

Distannabarrelenes with Three Coordinated SnII Atoms

Crystalline 1,4-distannabarrelene compounds [(ADC^Ar)₃Sn₂]SnCl₃ ( 3 - Ar ) (ADC^Ar={ArC(NDipp)₂CC}; Dipp=2,6-iPr₂C₆H₃, Ar=Ph or DMP; DMP=4-Me₂NC₆H₄) derived from anionic dicarbenes Li(ADC^Ar) ( 2 - Ar ) (Ar=Ph or DMP) have been reported. The cationic moiety of 3 - Ar features a barrelene framework with three coordinated Sn^II atoms at the 1,4-positions, whereas the anionic unit SnCl₃ is formally derived from SnCl₂ and chloride ion. The all carbon substituted bis-stannylenes 3 - Ar have been characterized by NMR spectroscopy and X-ray diffraction. DFT calculations reveal that the HOMO of 3 - Ph (ϵ=−6.40 eV) is mainly the lone-pair orbital at the Sn^II atoms of the barrelene unit. 3 - Ar readily react with sulfur and selenium to afford the mixed-valence Sn^II/Sn^IV compounds [(ADC^Ar)₃SnSn(E)](SnCl₆)_0.5 (E=S 4 - Ar , Ar=Ph or DMP; E=Se 5 - Ph ).     

Counting Radio-Krypton Atoms with a Laser

Because of their unique chemical and physical properties, long-lived rare krypton radioisotopes, ⁸⁵Kr and ⁸¹Kr, are ideal tracers for environmental samples, including air, groundwater and ice. Atom trap trace analysis (ATTA) is a new laser-based method for counting both ⁸⁵Kr and ⁸¹Kr atoms with the abundance as low as 10^-14 with micro-liters (STP) krypton gas. The entire system for rare radio-krypton measurement built at Hefei is presented, including the atom trap trace analysis instrument and sampling apparatus of gas extraction from water and krypton purification. Atmospheric⁸⁵Kr concentrations at different places in China were measured, showing a range of 1.3-1.6 Bq/m³, consistent with the northern hemispheric baseline. As a demonstration of the system, some shallow and deep groundwater samples in north and south China were sampled and dated.     

New Hexazirconium Clusters Containing Hydrogen Atoms

Reduction of ZrBr₄ with HSnBu₃ yielded a blue solid. When this blue solid was treated with PMe₃, a hexanuelear cluster [Zr₆Br₁₄H₄( PMe₃)₄] (2) was isolated. Reaction of the blue solid with [PPh₄]Br in CH₂Cl₂ resulted in the formation of a paramagnetic and unstable cluster anion, [Zr₆Br₁₈H₅]^2– (3), which disproportionated to form a new cluster anion, [Zr₆Br₁₈H₅]^3– (4) and some Zr(IV) species. Compounds containing 4 can also be obtained from reaction of the blue solid with Br^– in MeCN. Reduction of ZrCl₄ with HsnBu₃ gave a red–brown solid, and [Zr₆Cl₁₄H₄(AsMe₃)₄] (9) and [Zr₅Cl₁₂H₄(AsMe₃)₅](8) were obtained by reaction of the red–brown solid with AsMe₃. No cluster compounds containing amine ligands were obtained in the reaction of the red–brown solid with amines; only compounds containing the [Zr₆Cl₁₈ H₅]^3– anion and ammonium cations were isolated. Altogether ten products were characterized by single crystal X-ray diffraction and where possible, by ¹H NMR studies.     

The Chemi-Ionization Processes in Slow Collisions of Rydberg Atoms with Ground State Atoms: Mechanism and Applications

In this article the history and the current state of research of the chemi-ionization processes in atom–Rydberg atom collisions is presented. The principal assumptions of the model of such processes based on the dipole resonance mechanism, as well as the problems of stochastic ionization in atom–Rydberg atom collisions, are exposed. The properties of the collision kinetics in atom beams of various types used in contemporary experimentations are briefly described. Results of the calculation of the chemi-ionization rate coefficients are given and discussed for the range of the principal quantum number values 5 ≤ n ≤ 25. The role of the chemi-ionization processes in astrophysical and laboratory low-temperature plasmas, and the contemporary methods of their investigation are described. Also the directions of further research of chemi-ionization processes are discussed in this article.     

The Valence Orbitals of the Alkaline-Earth Atoms

Quantum chemical calculations of the alkaline-earth oxides, imides and dihydrides of the alkaline-earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca₆H₉[N(SiMe₃)₂]₃(pmdta)₃ (pmdta=N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n−1)d orbitals. The alkaline-earth metals Be and Mg build covalent bonds like typical main-group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline-earth metals, but are also very important for understanding and designing experimental studies.     

Optical Activity from Asymmetric Transition Metal Atoms

The preparation and resolution of asymmetric organometallic compounds of the transition series with four different ligands on the metal atom are described. Some of the optically active complexes retain their configuration, while others undergo racemization in solution. Their properties and reactions are discussed. Centers of asymmetry at transition metal atoms can also be detected on the basis of the magnetic nonequivalence of diastereotopic groups. Information about the configurational stability of such compounds can be obtained by investigation of the temperature dependence of the nuclear magnetic resonance spectra.     

Non-Bonded Radii of the Atoms Under Compression

Abstract : We present quantum mechanical estimates for non-bonded, van der Waals-like, radii of 93 atoms in a pressure range from 0 to 300 gigapascal. Trends in radii are largely maintained under pressure, but atoms also change place in their relative size ordering. Multiple isobaric contractions of radii are predicted and are explained by pressure-induced changes to the electronic ground state configurations of the atoms. The presented radii are predictive of drastically different chemistry under high pressure and permit an extension of chemical thinking to different thermodynamic regimes. For example, they can aid in assignment of bonded and non-bonded contacts, for distinguishing molecular entities, and for estimating available space inside compressed materials. All data has been made available in an interactive web application.     

Platinum Atoms Dispersed in Single-chain Polymer Nanoparticles

The intramolecular cross-linking of single polymer chains can form single-chain nanoparticles(SCNPs), which have many applications.In this study, styrenic copolymers with pendent triphenylphosphine as the coordination site for platinum ions(Pt(Ⅱ)) and benzocyclobutene as the latent reactive groups are synthesized. Triphenylphosphine groups in the chains can coordinate Pt(Ⅱ) and aid slight single-chain folding in dilute solution. The intramolecular cross-linking caused by the ring-open reaction of benzocyclobutene completes the single-chain collapse and forms stable SCNPs in dilute solution. Pt(Ⅱ) embedded in SCNPs can be further reduced to platinum atoms(Pt(0)). Pt(0) steadily and atomically dispersed in SCNPs exhibits better catalytic properties than normal polymer carried platinum particles do for the reduction of p-nitrophenol to p-aminophenol.     

Theoretical Calculations of Combination of Hydrogen Atoms

A resonance-complex set was developed to investigate the process of combination of hydrogen atoms with a modified resonance-complex theory and Monte-Carlo trajectory method over the temperature range 40-300 K. The obtained ratios of ortho to para at 300 K and at 77 K agree satisfactorily with experimental results. Unlike previous results, a maximum of the rate coefficient as a function of temperature is found near 150 K.