Local structure and dynamics of benzene confined in the IRMOF-1 nanocavity as studied by molecular dynamics simulation.

The local structure and dynamic behaviour of a benzene molecular assembly confined within the nano-cavities of a zinc-based metal-organic framework, [Zn(4)O(CO(2)C(6)H(4)CO(2))(3)](n) (IRMOF-1), were investigated by means of molecular dynamics (MD) simulations. The local structure of the confined benzene molecules was evaluated using radial distribution functions. The sites for adsorption of benzene in IRMOF-1 were well defined by the simulation. The diffusion coefficients at ambient temperature suggested that the mobility of the confined benzene was high, comparable to the bulk fluid. Decreasing the temperature gave rise to the aggregation of benzene in the IRMOF-1 frameworks. Molecular aggregation was attributed to the localization of benzene in the large and the small cavities of IRMOF-1, respectively. Both the translational diffusion coefficient and the trajectory of benzene provided evidence that the localization of benzene in the large and the small cavities takes place at ca. 200 K. Furthermore, at high benzene loading, the migration of benzene in the small cavities was prevented (frozen) below 135 K. Thus, the translational degree of freedom of the benzene molecules changed drastically, depending on the temperature.

Dispersions of image potential states on surfaces of clean graphite and lead phthalocyanine film.

Dispersions of image potential states on a graphite surface (denoted IPS1) and on 1 monolayer (ML) film (denoted IPS2) of lead phthalocyanine (PbPc) are investigated by the micro-spot angle-resolved two-photon photoemission (micro-AR-2PPE) spectroscopy. On the graphite surface, whole dispersions of the two members of IPS1 (n = 1 and 2) are observed. The n = 1 IPS1 peak is weakly visible at energy higher than the vacuum level. The effective mass of an electron in the n = 1 IPS1 becomes slightly light at the high momentum region, suggesting the interaction between the IPS1 and the unoccupied σ-band of graphite. On the PbPc film, the IPS2 band forms a band gap and back-folds at the boundary of the Brillouin zone. A 1-dimensional Kronig-Penny model is used to reproduce the effective mass and the shift of binding energy.

2H NMR study of 2D melting and dynamic behaviour of CDCl3 confined in ACF nanospace.

Two-dimensional melting of trichloromethane (chloroform) confined in activated carbon fibre was investigated using differential thermal analysis and (2)H NMR techniques. Differential thermal analysis revealed a thermal anomaly with an endothermic peak at 269 K, which was distributed from 250 K to 287 K on the heating direction. This anomaly was also observed upon cooling at the same temperature. Furthermore, (2)H NMR revealed that slow motion such as molecular hopping and/or diffusion of CDCl(3) in ACF affected the spectral line width. The temperature dependence (Arrhenius plot) of the spectral line width showed an inflection point at 227 K. The activation energy of molecular motion of CDCl(3) in ACF was 4 kJ mol(-1) at temperatures greater than 227 K and 7.7 kJ mol(-1) at temperatures less than 227 K. Reduction of the activation energy suggests that the average intermolecular distance between CDCl(3) molecules enlarges above the inflection point. The difference of activation energy (3.7 kJ mol(-1)) is close to the enthalpy of fusion in typical plastic crystals. These results reveal that the thermal anomaly and the transition of dynamic process correspond respectively to melting of CHCl(3) in ACF and the pre-melting phenomenon.

ESR study of molecular dynamics and orientation of TEMPO included in organic 1-D nanochannel.

A mixture of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical and 2,2,6,6-tetramethyl-1-piperidine (TEMP) was included into organic 1-D nanochannels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) crystal. Dilution of the paramagnetic TEMPO radical was achieved with excess TEMP, thereby isolating a TEMPO molecule in the nanochannel. For inclusion compounds of TPP with TEMPO and TEMP (TEMPO/all guest compounds = 0.017, and 0.15), temperature-dependent electron spin resonance (ESR) spectra were observed to investigate their molecular dynamics and orientation. In the temperature range from 112 K to room temperature, the spectra depended remarkably on the temperature. Temperature dependence was well interpreted by uniaxial rotation, suggesting that TEMPO molecules undergo uniaxial rotation about a channel axis with a molecular orientation in which the N-O bond in the nitroxide group is perpendicular to the channel axis. The activation energy of uniaxial rotation was evaluated as 4.5 +/- 0.3 kJ mol(-1).

Local structure of xenon adsorbed in the nanospaces of zeolites as studied by high-pressure 129Xe NMR.

Pressure (0-10 MPa) and local density dependence of 129Xe NMR chemical shift of xenon in various microporous materials was investigated using an in situ high-pressure probe. The density dependence of the chemical shift was analyzed using virial expansion of the chemical shift by xenon density. Results indicate that the second virial coefficient depends on the pore size and shape, and that the void space affects xenon-xenon interaction in both microporous and mesoporous materials. Furthermore, to interpret the magnitude of the virial coefficient in terms of the local structure of the adsorbed xenon, we analyzed the local structure of adsorbed xenon in molecular sieve 5A using Xe(n) clusters, thereby allowing description of the density dependence of the chemical shift. We also demonstrated the cluster model's validity by applying it to molecular sieves 13X and ZSM-5. The latter showed that the adsorbed xenon exists as a xenon monomer up to the filling of about 0.6 in micropores. Larger xenon clusters up to n = 4 have been grown with increasing filling of xenon. According to analyses using the Xe(n) cluster model, the second virial coefficient is related closely with the xenon cluster size, which contributes greatly to the chemical shift in the low loading region.