Changing Rules of Bonding Electron Pair Correlation Energies of CH_3X (X=F,OH,NH_2) Systems

The pair correlation energy of bonding electrons is used and analyzed in the cal- culation of CH and CY (Y = F, O, N) bonding electron pairs in CH3X (X = F, OH, NH2) isoelec- tronic systems based on intra- and interpair correlation energy results at both MP2-OPT2/6- 311++G(d) and MP2-OPT2/cc-pVtz levels with MELD program. Comparison of two set results shows that cc-pVtz and 6-311++G(d) give more correlation energy of valence electrons and innermost core electron pairs, respectively in these systems, resulting that the total correlation energy with cc-pVtz basis of each system is larger than that with 6-311++G(d). Investigations of pair correlation energy show that with the decrease of electronegativity of X atom and the increase of H atoms in these CH3X (X = F, OH, NH2) systems, the pair correlation energy of 1sC2 of the C atoms is transferable, and the correlation energy of CH bonding electron pair with little changes is of approximate transferability, while those of CY (CF, CO, CN) bonding electron pair decrease in a large extent from CH3F through CH3OH to CH3NH2 molecules. It is suggested that the study of pair correlation energy of bonding electrons will further deepen the understanding of electron corre- lation effect from traditional chemical bonding concept.

Relative Irradiance Measurement and Bonding Configurations of Amorphous Fluorinated Carbon Films Deposited by Electron Cyclotron Resonance Plasma

a-C:F films are deposited by microwave electron cyclotron resonance (ECR)plasma chemical vapor deposition (CVD) using trifluoromethane (CHF3) and benzene (C6H6) as source gases at different microwave powers. The radicals in plasma originating from source gases dissociation are analyzed by relative irradiance measurement. The bonding configurations and binding state of a-C:F films are measured with Fourier-transformed infrared spectrometer (FTIR) and x-ray photoelectron spectroscopy (XPS). The results show that a-C:F films are mainly composed of CF radical at lower powers but of CF2 radical at higher powers. The deposition of films is related to the radicals generated in plasma and the main bonding configurations are dependent on the ratio of CF to CF2 radicals in films.

Covalent electron density analysis and surface energy calculation of gold with the empirical electron surface model

Based on the empirical electron surface model （EESM）,the covalent electron density of dangling bonds （CEDDB） was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculation results show that CEDDB has a great influence on the surface energy of various index surfaces and the anisotropy of the surface.The calculated surface energy is in agreement with experimental and other theoretical values.The calculated surface energy of the close-packed （111） surface has the lowest surface energy,which agrees with the theoretical prediction.Also,it is found that the spatial distribution of covalent bonds has a great influence on the surface energy of various index surfaces.Therefore,CEDDB should be a suitable parameter to describe and quantify the dangling bonds and surface energy of various crystal surfaces.

ELECTRONIC STRUCTURE AND BOND CHARACTER OF COMPLEXES OF RARE EARTH CHLORIDES WITH CROWN ETHERS

A series of lanthanide complexes LnCl_3·L(Ln=La,Pr,Nd;L=15-C-5 or 18-C-6)have been synthesized and their molecular configuration,electronic structure and bond character have been studied by XPS and quantum chemical calculation.The calculated results are in good agreement with that obtained in the experiments.Three Cl atoms are on the same side of Ln in LnCl_3·15-C-5 and the crown ring on the other side.forming a complex molecule with coordination number 8.LnCl_3·15-C-5 is easily hygroscopic in air because of its unsaturated coordination,which differs sharply from the stable Ln(NO_3)_3·15-C-5 com- plex of coordination number 11.The HOMO and neighboring occupied MOs are composed of Cl 3p and O2p, and the LUMO and neighboring unoccupied MOs are composed of Ln orbitals.The level structure easily pro- duces Ln3d satellite in XPS caused by L→Ln charge transfer transition.Due to the coordination,the absolute values of the charge are decreased at Ln and O atoms,but increased at Cl atoms,which is in agreement with XPS results.

LOCALIZED STUDIES ON ELECTRONIC STRUCTURE AND CHEMICAL BOND FOR [NCCuS_2MoS_2]^(2-) CLUSTER

The canonical and locatized molecutar orbiters of [NCCuS_2NoS_2]^(2-) cluster were calculated by means of CNDO quantum chemistry method. Then the energy and properties of corresponding chemicat bonds were discussed, especially, Cu-Sb-No three center conjugated π bonds and No-St-No conjugated π bonds were accounted for.

Hybridized valence electrons of 4f^(0-14)5d^(0-1)6s^2:the chemical bonding nature of rare earth elements

The chemical bonding nature of rare earth（RE） elements can be studied by a quantitative analysis of electron domain of an atom. The outer electrons of RE elements are within the valence shell 4f^（0-14）5d^（0-1）6s^2, which are involved in all chemical bonding features. We in this work found that the chemical bonding characteristics of 4f electrons are a kind of hybridizations, and classified them into three types of chemical bonding of 4f^（0-14）5d^（0-1）6s^2, furthermore, the coordination number ranging from 2 to 16 could thus be determined. We selected Y（NO_3）_3, La（NO_3）_3, Ce（NO_3）_3, YCl_3, LaCl_3, and CeCl_3 as examples to in-situ observe their IR spectra of chemical bonding behaviors of Y^（3＋）, La^（3＋） and Ce^（3＋） cations, which could show different chemical bonding modes of 4f and 5d electrons. In the present study, we obtained the direct criterion to confirm whether 4f electrons can participate in chemical bonding, that is, only when the coordination number of RE cations is larger than 9.

Electron beam surface heating-diffusion bonding:An effective joining method for aluminum alloy metal-matrix composite with high SiC volume

As a novel method to reduce the temperature during electron beam welding,and to subsequently inhibit interfacial reaction between SiC and Al matrix,the electron beam surface heating-diffusion bonding is proposed for joining SiC particle reinforced aluminum alloy metal-matrix composite of 45 vol.%SiC/2024 Al.The defocused electron beam was used to heat the base metal surface,and the simultaneous pressure was applied to the butt surface to achieve bonding.The base metals were successfully joined by diffusion.The maximum temperature of the whole joint was effectively decreased to less than 650°C.The Gibbs free energy change of interfacial reaction was calculated,meaning a positive value reaching 218 kJ/mol and a consequently prominent inhibitory effect on the formation of brittle Al_(4)C_(3)that was proved by microstructural observation.The tensile strength for the bonded joint was increased by 35%compared to that for ordinary welded joint.When the TC4 layer was added,TiC strengthening particles were formed with the deficiency of Al_(4)C_(3),corresponding to the significantly increased tensile strength of 63%of base metal(154 MPa).

Unusually high electron density in an intermolecular non-bonding region:Role of metal substrate

It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed.Here,we present a systematical density functional theory study on adsorbed bis（para-pyridyl）acetylene（BPPA） tetramer on Au（111） surface.We observed unusually high electron density between two head-to-head N atoms,an intermolecular ＂non-bonded＂ region,in adsorbed BPPA tetramer.This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA,as squeezed by a newly revealed N-Au-N threecenter bonding.This bond,together with the minor contribution from N...H-C intermolecular hydrogen bonding,shortens the N-N distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV,effectively to a surface-confined in-plane pressure.The overlapped non-bonding vvavefunction hybridization arising from the effective pressure induced by the N-Au-N three-center bonding,as not been fully recognized in earlier studies,was manifested in non-contact Atomic Force Microscopy.