Interaction potential for He-H2 in the region of the van der Waals minimum

Interaction energies for the He-H₂ system have been computed by a VB method for the intermolecular distances 5.2 ? R ? 20.0 bohr and two different orientations of the H₂ molecule (θ = 0°, 90°). The results, especially for the anisotropy, are in good agreement with experiment. The dispersion constants C₆ and C₈ and the corresponding anisotropy constants α₆ and α₈ are presented.     

Interaction potential for He/H2 including the region of the van der waals minimum

The energy of He/H₂ in its ground state is calculated in an ab-initio way using the IEPA PNO method for three different H-H distances, three different angles and for distances between He and the midpoint of H₂ ranging from 3 to 20a₀.A van der Waals minimum of ≈21°K is found for the linear arrangement and a saddle point of ≈14°K for the C_2v geometry. The computed hypersurface is compared with experiment and with the R^?6 term known from perturbation theory. The anisotropy of the potential is much larger than what is predicted asymptotically.     

Full CI calibration of model hamiltonian,large basis set studies of the H2-H2 van der Waals interaction.

The non-variational CEPA2 PNO ansatz, recently employed in detailed studies of the H₂-H₂ van der Waals interaction by Burton and Senff and the full CI extrapolation studies on the same system by Burton are discussed in relation to the explicit full CI study of Harrison and Handy for the planar T configuration of H₂-H₂ (R = 6.5 a_o) in a basis of 80 functions.     

Laser spectroscopic investigation of the X 2Σ1/2 state of the van der Waals molecule NaAr

The laser-excitation spectrum of the transition X ²Σ⁺ → A ²Π of NaAr has been investigated using a supersonic expansion of a mixture of sodium vapor and argon gas for production of the molecules. In comparison to preyous investigations the rotational constants of the vibrational levels ν″ = 2, 3 and 4 of the X ²Σ⁺ state could in addition be determined. From our results we deduce a value of R_e = 5.008(5) × 10^?10 m for the equilibrium internuclear distance and of D_e = 41.7(δ) cm^?1 for the well depth of the X ²Σ⁺ state.     

Photochemistry in van der Waals complexes: Observation of the intermediate state of the Hg*,Cl2 reaction

A novel method designed to observe the collision complex of a photochemical reaction is reported here. The reactants Hg, Cl₂ are frozen in a van der Waals complex (HgCl₂), and then promoted by an optical excitation (250 nm) to the reactive state. The broad complex action spectrum, presumably due to the Hg⁺-Cl₂^? intermediate, is monitored through the HgCl(B ²Σ⁺) fluorescence.     

Lithium ions in the van der Waals gap of Bi2Se3 single crystals

Insertion/extraction of lithium ions into/from Bi₂Se₃ crystals was investigated by means of cyclic voltammetry. The process of insertion is reflected in the appearance of two bands on voltammograms at ∼1.7 and ∼1.5 V, corresponding to the insertion of Li⁺ ions into octahedral and tetrahedral sites of the van der Waals gap of these layered crystals. The process of extraction of Li⁺ ions from the gap results in the appearance of four bands on the voltammograms. The bands 1 and 2 at ∼2.1 and ∼2.3 V correspond to the extraction of a part of Li⁺ guest ions from the octahedral and tetrahedrals sites and this extraction has a character of a reversible intercalation/deintercalation process. A part of Li⁺ ions is bound firmly in the crystal due to the formation of negatively charged clusters of the (LiBiSe₂.Bi₃Se₄⁻) type. A further extraction of Li⁺ ions from the van der Waals gap is associated with the presence of bands 3 and 4 placed at ∼2.5 and ∼2.7 V on the voltammograms as their extraction needs higher voltage due to the influence of negative charges localized on these clusters.     

Bi2SeO5: A single-crystalline van der Waals dielectric beyond h-BN

<正>1School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore;2CINTRA CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, Singapore 637553, Singapore     

Two Step Chemical Vapor Deposition of In2Se3/MoSe2 van der Waals Heterostructures

Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide interest not only for the fundamental research,but also for the application of next generation electronic and optoelectronic devices.Herein,we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In₂Se₃/MoSe₂ heterostructures.Transmission electron microscopy characterization reveals clearly that the In₂Se₃ has well-aligned lattice orientation with the substrate of monolayer MoSe₂.Due to the interaction between the In₂Se₃ and MoSe₂ layers,the heterostructure shows the quenching and red-shift of photoluminescence.Moreover,the current rectification behavior and photovoltaic effect can be observed from the heterostructure,which is attributed to the unique band structure alignment of the heterostructure,and is further confirmed by Kevin probe force microscopy measurement.The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.     

Augmented van der Waals equations of state: SAFT-VR versus Yukawa based van der Waals equation

Performance of the SAFT-VR equation of state developed for the hard sphere based simple fluids, namely the square-well, Sutherland and Yukawa fluids, is examined by comparing its results with simulation data and an augmented van der Waals (vdW) equation based on a Yukawa (Y) reference. Its shown that both for the equilibrium vapor-liquid data and data along selected isotherms in the liquid and supercritical fluid phases the vdW(Y) equation provides better results, particularly when going to lower temperatures.     

Van der Wals团簇ο-xylene N2的共振双光子电离光谱

The one-color resonant two -photon ionization technique is employed to study jetcooled van der Waals(vdW) complex o-xylene?N2 through the S0-S1 transition around the band. The spectra obtained exhibit rich information about the complex intermolecular vdW vibrational modes. We have tentatively assigned all the observed spectral features. The structure of the complex has been obtained by calculation of the minimum energy structure.     

Applications of an adiabatic rotational model to the Ar…O2 van der Waals molecule

In this paper a separation of vibrational and rotational motions is applied to describe the metastable levels of the ArO₂ van der Waals molecule. The potential energy surface is written as a sum of atom—atom pairwise Morse functions, the parameters being obtained by fitting the potential of Pirani and Vecchiocattivi at the equilibrium configuration. The results agree fairly well with experimental data about infrared absorption, assuming a J = 2 → 1 transition, where J is the quantum number associated to the total angular momentum of the complex. Also, close coupling three-dimensional calculations about the ArO₂ collision show a good agreement with some energies previously calculated. The widths for rotational predissociation have been estimated by this procedure to be of the order of 1 cm^?1.     

A possible transition state for the H2 + D2 exchange reaction

A proposal for a possible transition state for the H₂ + D₂ exchange reaction follows from an analysis of the Jahn-Teller instability of tetrahedral H₄. The suggested pathway involves pseudo-rotation in the e deformation space, with a compressed tetrahedral structure corresponding to the reaction saddle point.     

Mixed-pole terms in the anisotrophy of the long-range interaction coefficients for H2He and H2H2

It is shown that mixed-pole terms can make significant, and even dominant, contributions to the anisotropy of the long-range interaction C₈ coefficients for H₂He and H₂H₂.     

Accurate intermolecular ground state potential of the Ne-N2 van der Waals complex

Ab initio ground state potential energy surfaces are obtained from interaction energies calculated with the coupled cluster singles and doubles model including connected triples corrections [CCSD(T)] and the aug-cc-pVXZ (X=5,Q,T,D) basis sets augmented with two different sets of midbond functions (denoted 33221 and 33211). The aug-cc-pV5Z-33221 surface is characterized by a T-shaped 49.5 cm(-1) minimum at Re=3.38 Angstroms and a linear saddle point at 3.95 Angstroms with De=36.6 cm(-1). These results agree well with the values provided by the accurate semiempirical potentials available. The rovibronic spectroscopic properties are determined and compared to the available experimental data and previous theoretical results. We study the basis set convergence of the intermolecular potentials and the rotational frequencies. The aug-cc-pVTZ basis sets provide reasonable binding parameters, but seem not to be converged enough for the evaluation of the microwave spectra. The aug-cc-pVQZ basis sets considerably improve the triple zeta results. The differences between the results obtained with the aug-cc-pVTZ-33221 basis set surface and those with the aug-cc-pVQZ-33221 are smaller than those of the corresponding bases with the set of 33211 midbond functions. The aug-cc-pVQZ surfaces are close to the aug-cc-pV5Z, that are expected to be close to convergence. With our best surfaces the errors in the frequencies with respect to the accurate experimental results go down to 0.6%.     

Accurate intermolecular ground state potential of the Ar-N2 van der Waals complex

After carrying out a systematic basis set convergence study, we evaluate several ground state potential energy surfaces of the Ar-N(2) van der Waals complex at the coupled cluster singles and doubles model including connected triples corrections. We use the aug-cc-pVXZ (X=5,Q,D) and the daug-cc-pVQZ basis sets augmented with a set of 3s3p2d1f1g (denoted 33211) and 3s3p2d2f1g (denoted 33221) midbond functions, respectively. aug-cc-pVTZ-33211 results were available in the literature. The aug-cc-pV5Z-33211 (daug-cc-pVQZ-33221) surface is characterized by a T-shaped minimum at R(e)=3.709 (3.701) A and of 99.01 (102.50) cm(-1), and a linear saddle point at 4.260 (4.257) A and D(e)=75.28 (79.73) cm(-1). These results are compared with the values provided by the semiempirical potentials available, and those of previous theoretical studies. The basis set convergence of the intermolecular potentials is also analyzed. From the potentials the rovibronic spectroscopic properties are determined. We study the basis set convergence of the rotational frequencies. The binding parameters that characterized the aug-cc-pVTZ-33211 surface are reasonable, but the surface is not good enough to evaluate the microwave spectra. The aug-cc-pVQZ-33211 basis set results considerably improve the triple zeta and are close to the aug-cc-pV5Z-33211. Considering the small differences between the quadruple and the quintuple zeta surfaces, the latter results can be expected to be close to convergence. At this level the differences with respect to the accurate experimental frequencies are in the order of 0.7%. In the case of the daug-cc-pVXZ-33211,33221 (X=5,Q,T,D) series, the convergence of the interaction energies with respect to basis set improvement is not so smooth. The errors in the frequencies obtained with the daug-cc-pVQZ-33221 basis set with respect to experiment are in the order of 0.4%.     

The anisotropic van der waals potential for He-N2

We have calculated the spherical v₀ and anisotropic radial components v₂ and v₄ in the usual Legendre expansion for the rigid rotor He-N₂ potential using the method of Tang and Toennies Potential curves covering the range of internuclear distances from 2.5 to 8.0 Å, which includes the minimum region, arc presented and compared with a recent experimental potential derived from differential total cross sections.     

Ab initio calculations of H2-H2 potential surfaces near the van der Waals minimum

The interaction energy between two hydrogen molecules near the van der Waals minimum is computed, for four relative orientations, and for intermolecular distances ranging from 5.5 to 16 au. A partially optimized basis set limited to 52 independent gaussian functions was used throughout the energy calculations. A new method based on the polarized atomic orbital technique has been used to reduce subsequently the size of the CI calculations which makes this method tractable for heavier molecular systems than H₂-H₂.     

Ab initio calculations on the singlet and triplet energy surfaces for CsiH2

Singlet and triplet calculations, including configuration interaction, are reported for H₂CSi, HCSiH and CSiH₂, and for the transition state on both surfaces.     

A study of interaction in the lowest singlet and triplet states of H2

The potential energy curves of the ground state and the first excited state of H₂ are examined in terms of the electronic force acting on each nucleus. The results reveal the detailed course of events that occur when two hydrogen atoms with parallel and antiparallel electron spins approach one another from a large internuclear separation.     

CO/H2 and CO2/H2 reactions with amorphous carbon-metal catalysts

By metal impregnation of selected naturally occurring organic materials followed by controlled carbonization, metal semicoke catalysts can be readily prepared. These catalysts have been tested in the synthesis of hydrocarbons and alcohols from CO/H₂ and CO₂/H₂ mixtures. Fe and Co preparations have been used. Relatively high temperatures are required when using these catalysts, which are quite active for synthesis using CO₂ and H₂. The pressure (5150 kPa) is very favorable both for the synthesis of liquid hydrocarbons (C₅–C₃₀) and alcohols (C₁–C₅).

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. CO/H₂ CO₂/H₂. Fe Co. , CO₂ H₂. 5150 ) (C₅–C₃₀) (C₁–C₅).