Theoretical study on non-sequential double ionization of carbon disulfide with different bond lengths in linearly polarizedlaser fields

By using a two-dimensional Monte-Carlo classical ensemble method, we investigate the double ionization（DI） process of the CS_2 molecule with different bond lengths in an 800-nm intense laser field. The double ionization probability presents a ＂knee＂ structure with equilibrium internuclear distance R = 2.9245 a.u.（a.u. is short for atomic unit）. As the bond length of CS increases, the DI probability is enhanced and the ＂knee＂ structure becomes less obvious. In addition,the momentum distribution of double ionized electrons is also investigated, which shows the momentum mostly distributed in the first and third quadrants with equilibrium internuclear distance R = 2.9245 a.u. As the bond length of CS increases,the electron momentum becomes evenly distributed in the four quadrants. Furthermore, the energy distributions and the corresponding trajectories of the double-ionized electrons versus time are also demonstrated, which show that the bond length of CS in the CS_2 molecule plays a key role in the DI process.

Accelerating Oxygen Electrocatalysis Kinetics on Metal-Organic Frameworks via Bond Length Optimization

Metal-organic frameworks(MOFs)have been developed as an ideal platform for exploration of the relationship between intrinsic structure and catalytic activity,but the limited catalytic activity and stability has hampered their practical use in water splitting.Herein,we develop a bond length adjustment strategy for optimizing naphthalene-based MOFs that synthesized by acid etching Co-naphthalenedicarboxylic acid-based MOFs(donated as AE-CoNDA)to serve as efficient catalyst for water splitting.AE-CoNDA exhibits a low overpotential of 260 mV to reach 10 mA cm^(−2)and a small Tafel slope of 62 mV dec^(−1)with excellent stability over 100 h.After integrated AE-CoNDA onto BiVO_(4),photocurrent density of 4.3 mA cm^(−2)is achieved at 1.23 V.Experimental investigations demonstrate that the stretched Co-O bond length was found to optimize the orbitals hybridization of Co 3d and O 2p,which accounts for the fast kinetics and high activity.Theoretical calculations reveal that the stretched Co-O bond length strengthens the adsorption of oxygen-contained intermediates at the Co active sites for highly efficient water splitting.

Effects of Rotational Isomerism and Bond Length Alternation on Optical Spectra of FTC Chromophore in Solution

Rotational isomerism effects on the optical spectra of a push-pull nonlinear optical chro-mophore 2-dicyanomethylen-3-cyano-4-f2-[E-（4-N,N-di（2-acetoxyethyl）-amino）-phenylene-（3,4-dibutyl）-thien-5]-E-vinylg-5,5-dimethyl-2,5-dihydrofuran （FTC） in a few solvents have been studied using the time-dependent density functional theory in combination with the polarizable continuum model. It is shown that the maximum absorption peaks of the ro-tamers have difference of nearly 30 nm both in vacuum and in solutions. The population of the rotamers changes a lot in different solvents. Based on the geometries optimized by Hartree-Fock method, the Maxwell-Boltzmann averaged absorption has been calculated and the maximum absorption peak is in good agreement with experiment. It indicates that the bond length alternation can have an important effect on the optical spectra.

The Effect of Elevated Temperature on Bond Performance of Alkali-activated GGBFS Paste

The main reaction products were investigated by analysis of microstructure of alkali-activated ground granulated blast furnace slag （GGBFS） paste. An experimental research was performed on bond performance of alkali-activated GGBFS paste as a construction adhesive after exposure to 20-500℃. Through XRD analysis, a few calcium silicate hydrate, hydrotalcite and tetracalcium aluminate hydrate were determined as end products, and they were filled and packed each other at room temperature. In addition, akermanite dramatically increased at 800 ~C and above. The two key parameters, the ultimate load Pu.T and effective bond length Le, were determined using test data of carbon fiber-reinforced polymer （CFRP）-to-concrete bonded joints at elevated temperature. The experimental results indicate that the ultimate load Pu.T remains relatively stable initially and then decreases with increasing temperature. The effective bond length Le increases with increasing temperature except at 300℃. The proposed temperature-dependent effective bond length formula is shown to closely represent the test data.

Ion source effect on the bond length of ^4HeH^＋

The bond length of ^4HeH^＋ resulting from collision-induced destruction is measured at 1.4420 MeV using the Coulomb Explosion Technique. The measured bond length of ^4HeH^＋ is 0.094±0.003nm. The bond length of ^4HeH^＋ obtained with our radio frequency （RF） ion source is larger than that obtained with a duoplasmatron ion source at Argonne National Laboratory （ANL）, but the bond lengths of H^＋2 and H^＋3obtained separately by ANL and by us with the two different ion sources are consistent with each other, which implies that there exists an ion source effect on the bond length of ^4HeH^＋. The main reason why the 4^4HeH^＋ bond lengths obtained by the two different ion sources are different is also discussed.

Why Static O-H Bond Parameters Cannot Characterize the Free Radical Scavenging Activity of Phenolic Antioxidants: ab initio Study

The static O-H bond parameters including O-H bond length, O-H charge difference, O-H Mulliken population and O-H bond stretching force constant (k) for 17 phenols were calculated by ab initio method HF/6-31G**. In combination with the O-H bond dissociation enthalpies (BDE) of the phenols determined by experiment, it was found that there were poor correlationships between the static O-H bond parameters and O-H BDE. Considering the good correlationship bt tween O-H BDE and logarithm of free radical scavenging rate constant for phenolic antioxidant, it is reasonable to believe that the ineffectiveness of static O-H bond parameters in characterizing antioxidant activity arises from the fact that they cannot measure the O-H BDE.

A High-Precision Calculation of Bond Length and Spectroscopic Constants of Hg2 Based on the Coupled-Cluster Theory with Spin-Orbit Coupling

Based on the two-component relativistic effective core potential and matched basis sets cc-pwcvnz-pp （n=Q, 5）, combining the completed basis-set extrapolation of electronic correlation energy and the fourth-order polynomial fitting technique, the bond length and spectroscopic constants of Hg2 are studied by the coupled cluster theory with spin-orbit coupling. Spin-orbit coupling is included in the post Hartree-Fock procedure, i.e., in the coupled- cluster iteration, to obtain more reliable theoretical results. The results show that our theoretical values agree with the experimental values very well and will be helpful to understand the spectral character of Hg2.

The Coulombic Nature of the van der Waals Bond Connecting Conducting Graphene Layers in Graphite

Carbon forms a variety of compounds with single, double, triple and the intermediate resonance bonds with atoms of its own or other kinds. This paper is concerned with graphite, a very useful material, which is a stack of electrically conducting graphene layers held together by weak van der Waals (vdW) bonds. It crystallizes in hexagonal and rhombohedral forms, in which the hexagon inter-planar bond distance is 0.34 nm. Here a new and simple approach accounts for this bond length and shows the coulombic nature of the vdW bond.

High-intensity molecular harmonic generation without ionization

We theoretically investigate high-order harmonic generation from H ＋ 2 in an infrared laser field.Our numerical simulations show that a highly efficient plateau structure exists in the molecular harmonic spectrum.Under the action of the infrared laser pulse,the bound electronic wave packet in a potential well has enough time to tunnel through the effective potential barrier,which is formed by the molecular potential and the infrared laser field,and then recombine with the neighboring nucleus emitting a harmonic photon.During the entire dynamic process,because the wave packet is mainly located in the effective potential,the diffusion effect is of no significance,and thus a highly efficient harmonic plateau can be achieved.Specifically,the cut-off frequency of the plateau is linearly scaled with the peak amplitude of the infrared laser electric field,which may open another route to examine the internuclear distance of the molecule.Furthermore,one may detect the molecular bond lengths using the harmonic plateau.

Stresses induced by post-tensioned anchor in jointed rock mass

A new analytical study on stresses around a post-tensioned anchor in rocks with two perpendicular joint sets is presented. The assumptions of orthotropic elastic rock with plane strain conditions are made in derivation of the formulations. A tri-linear bond-slip constitutive law is used for modeling the tendon-grout interface behavior and debonding of this interface. The bearing plate width is also considered in the analysis. The obtained solutions are in the integral forms and numerical techniques that have been used for evaluation. In the illustrative example given, the major principal stress is compressive in the anchor free zone and compressive stress concentrations of 815 k Pa and 727 k Pa(for the anchor load of 300 k N) are observed under the bearing plate and the bond length proximal end, respectively. However, large values of tensile stresses with the maximum of-434 k Pa are formed at the bond length distal end. The results obtained using the proposed solution are compared very those of numerical method(FEM).

Activating Process of Geopolymer Source Material: Kaolinite

The calcining process was recorded by differential scanning calorimetry and ther-mogravimetry （DSC-TG）. The dehydroxylation （activating process） was partitioned into two steps by calculating and comparing the O-H bond lengths between inner hydroxyl group and surface hydroxyl group, as well as the ionic bond of Al-OH and position of -OH. X-ray diffraction （XRD） and compressive strength measurement show that the activity of calcined materials increases with the increasing of temperature in dehydroxylation region but decreases abruptly in the ＂spinel＂ region. The suggested temperature for activating kaolinite is 900 ℃ .

Effects of the structural order of canthaxanthin on the Raman scattering cross section in various solvents:A study by Raman spectroscopy and ab initio calculation

In this work,we measure the Raman scattering cross sections（RSCSs） of the carbon-carbon（CC） stretching vibrational modes of canthaxanthin in benzene,acetone,n-heptane,cyclohexane,and m-xylene.It is found that the absolute RSCS of CC stretching mode of canthaxanthin reaches a value of 10 24 cm ^-2 ·molecule ^-1 ·sr ^-1 at 8×10 ^-5 M,which is 6 orders of magnitude larger than general RSCS（10 30 cm 2 ·molecule 1 ·sr 1）,and the RSCSs of canthaxanthin in various solvents are very different due to the hydrogen bond.A theoretical interpretation of the magnetic experimental results is given,which is introduced in a qualitative nonlinear model of coherent weakly damped electron-lattice vibration in the structural order of polyene chains.In addition,the optimal structure and the bond length alternation（BLA） parameter of canthaxanthin are calculated using quantum chemistry calculation（at the b3lyp/6-31g（d,p） level of theory）.The theoretical calculations are in good agreement with the experimental results.Furthermore,the combination of Raman spectroscopy and the quantum chemistry calculation study would be a quite suitable method of studying the structures and the properties of the π-conjugated systems.

Extraction Difficulty of Lithium Ions from Various Crystal Planes of Lithium Titanate

To study the extraction difficulty of lithium ions from various crystal planes of Li2 TiO3, according to the first principle, four representative crystal surfaces of Li2TiO3（precursor）,（-133）,（-206）,（002） and（-131）, were selected to establish a model and to calculate the surface energy, bond length and population using Materials Studio 5.5（MS 5.5）. The results demonstrate that there is no direct relationship between the surface energy and the order of disappearance of the four diffraction peaks when lithium titanate is treated with hydrochloric acid, instead, the difficulty of Li~＋ extraction from various crystal faces corresponds to the Li-O bond strength. Lithium ion is easy to remove from（-133） and（-206） due to the relatively weak Li-O bond strength. In contrast, Li＋ extraction requires a longer time for（002） and（-131）.

Hydroxyl groups in nonmetamict chevkinite-(Ce): a crystal chemical discussion

The minerals of chevkinite group were commonly considered to be anhydrous minerals. The infrared absorption spectrum of natural nonmetamict chevkinite-（Ce） from the aegirine-alkali granite, Miannlng, Sichuan Province, China, exhibited two broad peaks in the 3600-2800 cm^-1 region owing to the OH stretching. The corresponding H20 content required for the charge balance in formula was 1.27%. The O-H. … O bond lengths maight cover from 0.2658 to 0.2794 nm by the correlated OH stretching energies. An electrostatic charge balance for chevkinite-（Ce） based on the assigned site-population from chemical data was calculated without the hydrogen contribution. The resulting empirical bond-valence sum on 06, 08, 02, 03, 05, and 04 ranged from 1.73 to 1.95 vu. The partial substitution of O by OH may occur in four atom sites： 06, 02, 04, and 05. The small differences in the bond-valence sums between the supposed donors and acceptors may mean a mixed donor/acceptor role of the involved oxygen atoms. The IR spectral features between 3394 and 3035 cm-1 consisted of various hydrous species at different structural sites and orientations. The OH groups in the chevkinlte-（Ce） appeared to be involved in local charge imbalance in the structure and to be present when the mineral crystallized hydrothermally.

Theoretical Studies on the First Hyperpolarizabilities of One-dimensional Donor-bridge-acceptor Chromophores and New Applications of BLA in Determining Molecular First Hyperpolarizabilities

We present a quantum-chemical analysis of the relationship between the bond length alteration （BLA） and the static first hyperpolarizability of a series of one-dimensional （1D） chromophores with donor-bridge-acceptor （D-B-A） structures. The calculated results show that the parameter BLA can be considered as an indicator to evaluate the molecular first hyper- polarizability. Along the direction of molecular ground-state dipole moments, the evolutions of BLA can be classified into three categories： the first is a non-monotonic line, which represents most chromophores; the second is monotonic increasing; and the third, contrarily, is monotonic decreasing. On the whole, the first hyperpolarizabilities of these studied chromophores are the monotonic functions of BLA along the direction of dipole moments. Therefore, the first hyperpolarizability of these 1D chromophores can be preliminarily evaluated in terms of the development of BLA without a rigorous computation. In other words, one can roughly estimate the relative magnitude of the first hyperpolarizability according to the optimized geometry.

Solvent Effects on Two-Photon Absorption of Alkyne and Alkene π-bridging Chromophores

The present work concerns the study of solvent effects on the geometrical structures, as well as one- and two-photon absorption （TPA） processes, for two series of alkyne and alkene π-bridging molecules, within the framework of the polarization continuum model. Particular emphasis was put on the characterization of solvent effects on the molecular geometrical structures and geometric distortion, which were measured by the bond-length-alternation parameter. The π centres in the compounds are seen to play a decisive role in increasing the TPA cross section and nonlinear optical properties. All studied molecules have relatively strong TPA characteristics, while the alkyne π-bridging ones yield larger TPA cross sections.

Crystal Chemistry of Iron in Non-Metamict Chevkinite-(Ce): Valence State and Site Occupation Proportions

The ideal formula for chevkinite can be expressed as A4BC2D2Si4O22. It is important to determine the valence state and site occupation proportions for Fe among the B, C, and D octahedral sites as it may help to identify different species in the chevkinite group. Non-metamict chevkinite-（Ce） from Mianxi alkali feldspar-granite, Sichuan Province, China, was investigated using Moessbauer spectroscopy. The Fe^3＋/∑Fe ratio was 39.2%. A significant increase of Fe^3＋ occured during metamictization and annealing for chevkinite-group minerals. In metamict samples Fe tended to lower coordination, According to the correlation between bond length and isomer shift （IS）, the quadrupole doublets with IS = 1.10 and 0.94 mm·s^-1 can be assigned to Fe^2＋ in the B and C octahedral sites, respectively. Based on the correlation between octahedral distortion and quadrupole splitting （QS）, the quadrupole doublets with QS = 0.86 and 0.77 mm·s^-1 can be assigned to Fe^3＋ in the C and D sites, respectively. The simplified formula can be revised as： Ce4Fe^2＋ （Ti, Fe^2＋, Fe^3＋ ）2（Ti, Fe^3＋ ）2Si4（O,OH）22. It indicated that the non-metamict chevkinite-（Ce） belonged to Fe^2＋ end member of the chevkinite group because Fe^2＋ was the predominant component in the B site.

The Curing Process and Elastic Modulus of HTPB-Containing Polyurethanes

By means of the functionality distribution deduced and weight averaged functionality a and molecular size vb2, the sol-gel distribution equations of HTPB(Hydroxyl terminated polybutadiene) + TDI (Toluene-2, 4-diisocyanate) expressed by the model of Aai-B2 type polycondensation were solved and the elastic modulus were calculated. The experimental results of HTPB+TDI curing process indicate that a, vb2 and functionality distribution function are available basically.

Electronic structures and phase transition characters of β-, P61-, P62- and δ-Si_3N_4 under extreme conditions: a density functional theory study

This paper describes the results of structural, electronic and elastic properties of silicon nitride （in its high-pressure P61 and P62 phases） through the first-principles calculation combined with an ultra-soft pseudo- potential. The computed equilibrium lattice constants agree well with the experimental data and the theoretical results. The strongest chemical bond （N-Si bond） shows a covalent nature with a little weaker ionic character. P61- Si3N4 is more stable than P62-Si3N4 due mainly to the fact that the shorter N-Si bond in the P61 phase allows stronger electron hybridizations. We have also predicted the phase stability of Si3N4 using the quasi-harmonic approximation, in which the lattice vibration and phonon effect are both considered. The results show that the 13 P61 phase transition is very likely to occur at 42.9 GPa and 300 K. The reason why the β→P61→3 phase transitions had never been observed is also discussed.

A Mssbauer effect study of Fe^(3+) bearing γ-Fe_(2)SiO_(4)

Three synthetic Fe3+ bearing λ-Fe2SiO4 were analyzed using electron probe method, and the M?ssbauer spectra of the samples at 298 K, 150 K, and 95 K were measured. Each spectrum at three temperatures is composed of two doublets. These two doublets are assigned to Fe2+ in the octahedral sites and Fe3+ in the tetrahedral sites, respectively. Site occupancies were determined. The results show that Fe3+ and a small amount of Si4+ are in the tetrahedral and octahedral sites, respectively. The average bond lengths of the octahedral and tetrahedral sites were calculated according to the equations primarily given by Hill et al., O’Neill and Navrotsky and modified by the authors. Furthermore, the octahedral and tetrahedral bond lengths were used to calculate cell parameters and oxygen parameters. In addition, Fe3+ line broadening in the M?ssbauer spectra of Fe3+ bearing λ-Fe2SiO4 were interpreted by using the next nearest neighbor effects