Particle nature of the photonic spin Hall effect.

It is widely recognized that light exhibits a wave-particle duality. However, the explanation for the photonic spin Hall effect (PSHE) primarily relies on the wave nature of light as dictated by Maxwell's Equations. There is a lack of exploration into the particle nature of light in this regard. In this context, we offer a fresh interpretation of the PSHE from the perspective of particle nature of light. For the out-of-plane PSHE, the spin shifts result from the macroscopic manifestation of the conservation of spin-orbital angular momentum of one photon. For the in-plane PSHE, the spin shifts arise from the spread of in-plane wavevector. Based on the wave nature of light, we also obtain the same spin shifts, confirming the consistency of the wave-particle duality of light. Furthermore, we find that the spin shifts of the PSHE are not the overall displacement of photons with the same handedness, but the outcome of coherent superposition among photons of the same handedness. These discoveries further enhance our comprehension of the fundamental nature of the PSHE.

Conservation of the Stokes-Einstein relation in supercooled water.

The Stokes-Einstein (SE) relation is commonly regarded as being breakdown in supercooled water. However, this conclusion is drawn by testing the validity of some variants of the SE relation rather than its original form, and it appears conflicting with the fact that supercooled water is in its local equilibrium. In this work, we show by molecular dynamics simulations that the Stokes-Einstein relation is indeed conserved in supercooled water. The inconsistency between the original SE relation and its variants comes from two facts: (1) the substitutes of the shear viscosity in the SE variants are only approximate relations; and (2) the effective hydrodynamic radius actually decreases with decreasing temperature, instead of being a constant as assumed in the SE variants.

The diffusion, structural relaxation, and fragility of [VIO2+][Tf2N-]2 ionic liquid.

Viologen-based ionic liquids can form various microscopic structures at different temperatures. In this work, the dynamics of dimethyl-viologen bis-(tetrafluoroborate) ([VIO2+][Tf2N-]2) ionic liquid within 400-800 K has been exploited by molecular dynamics simulations. [VIO2+][Tf2N-]2 exhibits a supercooled liquid analogous diffusion and structural relaxation even at temperature T = 400 K, and behaves more like simple liquids as temperature increases. The variation of the diffusion constant and structural relaxation time with temperature follows a super-Arrhenius law; both can be fitted by two Arrhenius laws with a crossover temperature or fitted by a VFT law. [VIO2+][Tf2N-]2 behaves as a fragile glass former. The decoupling of diffusion and relaxation is observed in [VIO2+] but not in [Tf2N-]. The variation of dynamics with temperature is attributed to the time differences of the persistence in ion cage and exchange out of ion cage.

Effect of external static electric fields on the dynamic heterogeneity of ionic liquids.

Ionic liquids (ILs) exhibit behavior analogous to supercooled liquids at room or even higher temperatures. ILs usually work under an externally applied static electric field (E). In this work, molecular dynamics simulations were performed with 1-ethyl-3-methyl-imidazolium tetrafluorborate ([EMI+][BF4-]) under E, with the aim of discovering the influence of E on the dynamic heterogeneity of ILs. ILs show more homogeneous dynamics with increasing E, as indicated by non-Gaussian parameters and dynamic susceptibility. The dynamic heterogeneity is greater in the E direction than that in the perpendicular directions under the same E. Despite the dynamic heterogeneity, only a small decoupling between diffusion and relaxation is observed under E.

Dynamic heterogeneity in aqueous ionic solutions.

It is well known that supercooled liquids have heterogeneous dynamics, but it is still unclear whether dynamic heterogeneity also exists in aqueous ionic solutions at room or even higher temperatures. In this work, taking KSCN aqueous solutions as an example, we identify by molecular dynamics simulation that dynamics of ionic solutions at a finite concentration are heterogeneous at room and even higher temperatures. Our results indicate that thermal movements of K+ and SCN- deviate from the Gaussian distribution in time and space, as demonstrated by a non-Gaussian parameter and the self-van Hove function. The dynamic susceptibility is nonzero at intermediate times for both K+ and SCN-. The self-intermediate scattering function of ions decays in a stretched exponential way with an exponent smaller than one. The dynamics of the solution are more homogeneous at a higher temperature. Since transient ion clusters of different sizes decay with different lifetimes and exponents, we propose that the dynamic heterogeneity is introduced by transient cluster formation and dissociation in ionic solutions, which leads to a mixed relaxation scenario. Variants of the Stokes-Einstein relation are found to break down into a fractional form analogous to supercooled liquids, but the original Stokes-Einstein relation is indeed valid if taking into account the temperature dependence of the effective hydrodynamic radius. Overall, despite some quantitative differences, the dynamic heterogeneity in aqueous ionic solutions at room or higher temperatures is qualitatively analogous to that in supercooled liquids at a much lower temperature.

Roads to pentazolate anion: a theoretical insight.

The formation mechanism of pentazolate anion (PZA) is not yet clear. In order to present the possible formation pathways of PZA, the potential energy surfaces of phenylpentazole (PPZ), phenylpentazole radical (PPZ-R), phenylpentazole radical anion (PPZ-RA), PPZ and m-chloroperbenzoic acid (m-CPBA), p-pentazolylphenolate anion (p-PZPolA) and m-CPBA, and p-pentazolylphenol (p-PZPol) and m-CPBA were calculated by the computational electronic structure methods including the hybrid density functional, the double hybrid density functional and the coupled-cluster theories. At the thermodynamic point of view, the cleavages of C-N bonds of PPZ and PPZ-R need to absorb large amounts of heat. Thus, they are not feasible entrance for PZA formation at ambient condition. But excitation of PPZ and deprotonation of PPZ-RA probably happen before cleavage of C-N bond of PPZ at high-energy condition. As to the radical anion mechanism, the high accuracy calculations surveyed that the barrier of PZA formation is probably lower than that of dinitrogen evolution, but the small ionization potential of PPZ-RA gives rise to the unstable ionic pair of sodium PPZ at high temperature. In respect of oxidation mechanism, except for PPZ, the reactions of p-PZPolA and p-PZPol with m-CPBA can form PZA and quinone. The PZA formations have the barriers of about 20 kcal mol-1 which compete with the dinitrogen evolutions. The stabilities of PZA in both solid and gas phases were also studied herein. The proton prefers to transfer to pentazolyl group in the (N5)6(H3O)3(NH4)4Cl system which leads to the dissociation of pentazole ring. The ground states of M(N5)2(H2O)4 (M = Co, Fe and Mn) are high-spin states. The pentazolyl groups confined by the crystal waters in the coordinate compounds can improve the kinetic stability. As to the reactivity of PZA, it can be persistently oxidized by m-CPBA to oxo-PZA and 1,3-oxo-PZA with the barriers of about 20 kcal mol-1.

Synthesis and crystal structure of deca-carbon-yl(µ3-3,7-di-thia-nonane-1,9-di-thiol-ato)bis-(µ2-propane-1,3-di-thiol-ato)nickel(II)tetra-iron(II) di-chloro-methane disolvate.

The title compound,, [Fe4Ni(C3H6S2)2(C7H14S4)(CO)10]·2CH2Cl2, is reported as a biomimic model for the active site of [FeFe]-hydrogenases. Bis(2-mercaptoeth-yl)-1,3-propane-dithio ether nickel(II) was firstly introduced into [Fe2(C3H6S2)(CO)5] as an S-containing ligand. It coordinates with two [Fe2(C3H6S2)(CO)5] groups, and a five-metal core complex is formed. The Fe2S2 core is in a butterfly conformation. The Fe-Fe distances in the [Fe2(C3H6S2)(CO)5] groups are 2.5126 (6) and 2.5086 (7) Å. The distances between the adjacent Fe and Ni atoms are 3.5322 (1) and 3.5143 (1) Å. There are intra-molecular C-H⋯O and C-H⋯S contacts present in the complex. In the crystal, the five metal cores are linked via C-H⋯O hydrogen bonds, forming columns lying parallel to (110). The di-chloro-methane solvent mol-ecules are each partially disordered over two positions and only one is linked to the five-metal core complex by a C-H⋯O hydrogen bond.

Crystal structure and electrochemical properties of [Ni(bztmpen)(CH3CN)](BF4)2 {bztmpen is N-benzyl-N,N',N'-tris-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine}.

The mononuclear nickel title complex (acetonitrile-κN){N-benzyl-N,N',N'-tris-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine}-nickel(II) bis-(tetra-fluor-ido-borate), [Ni(C30H35N5)(CH3CN)](BF4)2, was prepared from the reaction of Ni(BF4)2·6H2O with N-benzyl-N,N',N'-tris-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine (bztmpen) in aceto-nitrile at room temperature. With an open site occupied by the aceto-nitrile mol-ecule, the nickel(II) atom is chelated by five N-atom sites from the ligand and one N atom from the ligand, showing an overall octa-hedral coordination environment. Compared with analogues where the 6-methyl substituent is absent, the bond length around the Ni2+ cation are evidently longer. Upon reductive dissociation of the acetro-nitrile mol-ecule, the title complex has an open site for a catalytic reaction. The title complex has two redox couples at -1.50 and -1.80 V (versus Fc+/0) based on nickel. The F atoms of the two BF4- counter-anions are split into two groups and the occupancy ratios refined to 0.611 (18):0.389 (18) and 0.71 (2):0.29 (2).

Crystal structure of [Cu(tmpen)](BF4)2 {tmpen is N,N,N',N'-tetra-kis-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine}.

The mononuclear copper title complex {N,N,N',N'-tetra-kis-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine-κ6N}copper(II) bis-(tetra-fluorido-borate), [Cu(C30H36N6)](BF4)2, is conveniently prepared from the reaction of Cu(BF4)2·6H2O with N,N,N',N'-tetra-kis-[(6-methyl-pyridin-2-yl)meth-yl]ethane-1,2-di-amine (tmpen) in aceto-nitrile at room temperature in air. The complex shows a distorted octa-hedral environment around the CuII cation (site symmetry 2) and adopts the centrosymmetric space group C2/c. The presence of the 6-methyl substituent hinders the approach of the pyridine group to the CuII core. The bond lengths about the CuII atom are significantly longer than those of analogues without the 6-methyl substituents.

Effect of Ion Rigidity on Physical Properties of Ionic Liquids Studied by Molecular Dynamics Simulation.

In this work, we have performed molecular dynamics (MD) simulations to compare the structural and dynamical properties of three ionic liquids (ILs), 1-ethyl-3-methyl-imidazolium tetrafluorborate ([EMI(+)][BF4(-)]), 1,1'-dimethyl-4,4'-bipyridinium bis(tetrafluorborate) ([VIO(2+)][BF4(-)]2), and 1,1'-dimethyl-4,4'-bipyridinium bis(trifluoromethylsulfonyl)imide (bistriflimide in short) ([VIO(2+)][Tf2N(-)]2), aiming to discover the influence of ion rigidity on the physical properties of ILs. [VIO(2+)] is more rigid than [EMI(+)], and [BF4(-)] is more rigid than [Tf2N(-)]. [VIO(2+)][BF4(-)]2 has an anion distribution different from the other two by the higher and sharper peaks in the cation-anion radial distribution functions, reflecting a close-packed local structure of anions around cations. [VIO(2+)][BF4(-)]2 and [VIO(2+)][Tf2N(-)]2 have similar dynamics much slower than [EMI(+)][BF4(-)], and [VIO(2+)][Tf2N(-)]2 shows a more isotropic molecular distribution than [VIO(2+)][BF4(-)]2 and [EMI(+)][BF4(-)]. Additionally, we have simulated two modified viologen-based ILs to reinforce our interpretations. We conclude from the above simulation results that the rigidity of anions influences the alignment of cations and that the rigidity of cations shows a large obstacle to their rotational capacity. Moreover, we have observed a slower diffusion of [VIO(2+)][BF4(-)]2 due to the electrostatic correlations, which stabilizes the ion-cage effect.

Structural, dynamic, and transport properties of concentrated aqueous sodium chloride solutions under an external static electric field.

In the absence of an external electric field, it has already been known that ion clusters are formed instantaneously in moderately concentrated ionic solutions. In this work, we use molecular dynamics (MD) simulations to investigate the changes of structural, dynamic, and transport properties in a sodium chloride solution under an external electric field from the ion cluster perspective. Our MD simulation results indicate that, with a strong external electric field E (≥0.1 V/nm) applied, ion clusters become smaller and less net charged, and the structures and dynamics as well as transport properties of the ion solution become anisotropic. The influence of the cluster structure and shell structure to transport properties was analyzed and the Einstein relation was found invalid in this system.

Slow light based on coherent hole-burning in a Doppler broadened three-level Lambda-type atomic system.

We show theoretically that the propagation of light can be slowed down considerably using the method of coherent hole-burning in a Doppler broadened three-level lambda-type atomic medium without the Doppler-free configurations. The reduction of group velocity of light pulse is achieved by the application of a saturating beam and a strong coupling beam which produce a narrow spectral hole-burning at resonance. We can obtain a larger group index than that using the method of saturation absorption spectroscopy in Doppler-broadened two-level atomic systems.