The adsorption properties of methane (CH4) have a great influence on shale gas exploration and development. The surface chemistry characteristics of nanopores are key factors in adsorption phenomena. The clay pores in shale formations exhibit basal surface and edge surfaces (mainly as A and C chain and B chain surfaces in illite). Little research regarding CH4 adsorption on clay edge surfaces has been carried out despite their distinct surface chemistries. In this work, the adsorption of CH4 confined in nanoscale illite slit pores with basal and edge surfaces was investigated by grand canonical Monte Carlo and molecular dynamics simulations. The adsorbed phase density, adsorption capacity, adsorption energy, isosteric heat of adsorption, and adsorption sites were calculated and analyzed. The simulated adsorption capacity compares favorably with the available experimental data. The results show that the edge surfaces have van der Waals interactions that are weaker than those of the basal surfaces. The adsorption capacity follows the order basal surface > B chain surface > A and C chain surface. However, the differences of adsorption capacity between these surfaces are small; thus, edge surfaces cannot be ignored in shale formation. Additionally, we confirmed that the adsorbed phase has a thickness of approximately 0.9 nm. The pore size determines the interaction overlap strength on the gas molecules, and the threshold value of the pore size is about 2 nm. The preferential adsorption sites locate differently on edge and basal surfaces. These findings could provide deep insights into CH4 adsorption behavior in natural illite-bearing shales.

The spontaneous polarized Raman spectra of normal and deuterated alcohols (C2-C5) have been recorded in the C-H stretching region. In the isotropic Raman spectra, a doublet of -CαH stretching vibration is found for all alcohols at below 2900 cm(-1) and above 2950 cm(-1). By comparing the experimental and calculated spectra of various deuterated alcohols, the doublets are attributed to the -CαH stretching vibration of different conformers. For ethanol, the band observed at 2970 cm(-1) is assigned as the stretching vibration of -CαH in the Cα-O-H plane of the gauche-conformer, while the band at 2895 cm(-1) is contributed from both the -CαH2 symmetrical stretching vibration of the trans-conformer and the -CαH stretching vibration out of the Cα-O-H plane of the gauche-conformer. The population of gauche-conformer is estimated to be 54% in liquid ethanol. For the larger alcohols, the same assignments for the doublet are obtained, and the populations of gauche-conformers with plane carbon skeleton are found to be slightly larger than that of ethanol, which is consistent with results from molecular dynamics simulations.

As an extension of the superatom concept, a new concept "isosuperatom" is proposed, reflecting the physical phenomenon that a superatom cluster can take multiple geometrical structures with their electronic structures topologically invariant. The icosahedral and cuboctahedral Au13(5+) units in the Au25(SCH2CH2Ph)18(-), Au23(SC6H11)16(-) and Au24(SAdm)16 nanoclusters are found to be examples of this concept. Furthermore, two isosuperatoms can combine to form a supermolecule. For example, the structure of the {Ag32(DPPE)5(SC6H4CF3)24}(2-) nanocluster can be understood well in terms of a Ag22(12+) supermolecule formed by two Ag13(8+) isosuperatoms. On the next level of complexity, various combinations of isosuperatoms can lead to supermolecules with different geometrical structures but similar electronic structures, i.e., "isosupermolecules". We take two synthesized nanoclusters Au20(PPhpy2)10Cl4(2+) and Au30S(StBu)18 to illustrate two Au20(6+) isosupermolecules. The proposed concepts of isosuperatom and isosupermolecule significantly enrich the superatom concept, give a new framework for understanding a wide range of nanoclusters, and open a new door for designing assembled materials.

To explore the possible existence of boron clusters without carbon analogs, we study B(84) cluster as a prototypical system by ab initio calculations. Structures of several isomer forms of B(84) are optimized. Among these isomers, a group of amorphous (disordered) structures are found to be the most stable. Different from the high-symmetry isomers, the amorphous B(84) clusters are more stable than the fullerene B(80) in terms of cohesive energy per atom. These amorphous structures can be distinguished from other high-symmetry structures experimentally via, for example, infrared spectra. The radial and angular distribution functions of amorphous B(84) structures are more diffuse than those of high-symmetry structures. On the basis of these findings, we propose that amorphous structures may be generic for boron and dominate boron clusters in a range of cluster scale.

Graphene molecules, hexafluorotribenzo[a,g,m]coronene with ncarbon alkyl chains (FTBC-Cn, n ‫؍‬ 4, 6, 8, 12) and Janus-type ''double-concave'' conformation, are used to fabricate self-assembly on highly oriented pyrolytic graphite surface. The structural dependence of the self-assemblies with molecular conformation and alkyl chain is investigated by scanning tunneling microscopy and density functional theory calculation. An interesting reverse face ''up-down'' way is observed in FTBC-C4 assembly due to the existence of hydrogen bonds. With the increase of the alkyl chain length and consequently stronger van der Waals interaction, the molecules no longer take alternating ''up-down'' orientation in their self-assembly and organize into various adlayers with lamellar, hexagonal honeycomb, and pseudohoneycomb structures based on the balance between intermolecular and molecule-substrate interactions. The results demonstrate that the featured ''double-concave'' molecules are available block for designing graphene nanopattern. From the results of scanning tunneling spectroscopy measurement, it is found that the electronic property of the featured graphene molecules is preserved when they are adsorbed on solid surface.graphene molecule ͉ Janus-type double-concave conformation ͉ scanning tunneling microscopy ͉ self-assembly A graphene molecules is composed of fused aromatic sets and is regarded as graphite subunit. After the success in theoretical prediction and experimental realization of graphene, graphene type molecules attract a great deal of interest (1-4). Their unique structures provide them promising potentials in micro/nano electronic devices (5-7). Continuous effort in chemical synthesis of graphene type molecules has produced various graphene molecules with the structures and properties beyond simple graphene. For example, polycyclic aromatic hydrocarbons (PAHs) compounds belong to a class of important functional graphene molecules (7,8). PAHs and their derivatives contain 2D subsections of graphene and show significant advantages, such as good solubility and ability to bear different chemical functionalities in their periphery with various electronic properties. These graphene molecules are promising candidates as building block for nanodevices through self-assembled architectures on 2D solid surfaces (9, 10).As a powerful tool for nanoscience and nanotechnology, scanning probe microscopy, in particular, scanning tunneling microscopy (STM) studies have produced images of the molecular self-assembly of graphene molecules at atomic/submolecular resolution, providing molecular understanding of intermolecular interactions and origin of their physical/chemical properties (11)(12)(13)(14). Because of their chemical structures, most of PAHs have a planar conformation and are inclined to form well-defined long-range self-assemblies on various substrates, such as gold and highly oriented pyrolytic graphite (HOPG). For examples, an alkyl-substituted PAH with D 2h symmetry and 78 carbon atoms in the aromatic core can se...

The micro-structure of hydration shell of solute in water is significant for understanding the properties of aqueous solutions. However the spectra of hydration shell are difficult to be obtained. Herein, a novel Raman ratio spectra, which is obtained through dividing the Raman spectra of aqueous solutions from the spectrum of water, was applied to deduce the spectra of hydration shell of organic (acetone-D6) and inorganic compounds (NaNO 3 , NaSCN, NaClO 4 , Na 2 SO 4 , NaCl) in water. Those spectra of the hydration shell were employed to study the micro-structures of the first hydration shells of anions, the number of water molecules in the first hydration shell of free anions and acetone-D6, and the aggregation behavior of ions in the concentrated aqueous NaNO 3 . The number of water molecules in the hydration shell was supported by our molecular dynamic simulations. The Raman ratio spectra can be widely employed to obtain the spectra of the first hydration shell, and it is helpful to understand the micro-structure of aqueous solutions.

Density functional calculations are performed to study the linear OCuO molecule in the neutral, cationic, and anionic charge states. The equilibrium bond lengths, vibrational frequencies, and electronic configurations are obtained. A theoretical assignment for the features in the photoelectronic spectrum is given at the local spin-density approximation level. Our results compare well with the available experimental results and show that the ground state of the OCuO molecule is the doublet (2Πg).

The electronic and magnetic properties of Co-doped ZnO are investigated based on the B3LYP hybrid spin-density functional method. The calculated electronic structures obtained from B3LYP agree well with the experimental results. B3LYP predicts that antiferromagnetic (AFM) ordering between the Co ions is favored over ferromagnetic (FM) ordering in intrinsic Co-doped ZnO, and reveals that the FM ordering can be induced by electron doping when the doping level reaches 1 electron per Co ion. These results agree well with the FM ordering observed in highly conductive n-type Zn1−xCoxO films. Charge transfer to the minority-spin d states of Co atoms and the consequent double-exchange interaction are the primary origins of FM ordering. Since Ni has one more electron than Co, we also investigate the electronic and magnetic properties of intrinsic Ni-doped ZnO. Qualitatively different from the local-density-approximation results, B3LYP predicts that Ni-doped ZnO is an insulator and favors AFM ordering.