Molecular dynamics simulations have been carried out for liquid–vapor interface of water and also of Lennard-Jones system. Surface tension and surface excess energy are calculated, from which surface excess entropy is evaluated. These thermodynamic quantities suggest the existence of some liquid-structural change near the surface of water, which is not seen in Lennard-Jones system. For water, orientational structuring near the surface is studied and two types of orientation are found. In the vapor side, a water molecule has a tendency of projecting one hydrogen atom toward the vapor, and in the liquid side, a molecule prefers to lie down on the surface with both hydrogen atoms slightly directed to the liquid. From these results, surface potential χ can be evaluated to be about +0.16 V at T=300 K, which confirms recent experimental results. The ellipticity coefficient is also discussed and the assumption often used in analysis of experimental results of ellipsometry is found to be inadequate for water due to the structural change. These observed orientational orderings are qualitatively consistent with results of molecular theory of surface recently developed and also with simulational results of water near hydrophobic walls.

Results of molecular dynamics computer simulation are presented for liquid–vapor interface of water–methanol mixture of various compositions at room temperature. The composition dependence of calculated surface tension is typical of aqueous solutions of organic compounds. The outermost surface layer is saturated with methanol even at low bulk concentrations of methanol. The density profile of each component seems oscillatory at some compositions.

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A Fourier transform infrared (FT-IR) spectrometer equipped with a microscopic accessory was used to monitor the cellulose crystalline structure at each developmental stage of coniferous tracheid cell wall formation. The spectra showed that the cellulose in the primary cell wall was rich in the metastable Iα crystalline form and interestingly had a higher crystallinity than the secondary wall cellulose composed mainly of the stable Iβ crystalline phase. These results indicate the presence of an in vivo physical force at the cell surface which may stress the primary wall cellulose during the crystallization. Moreover, the primary wall cellulose was oriented parallel to the enlarging direction of growing cells. Thus, we consider that the cellular growing stress generated between the plasma membrane and the primary wall may elongate just-biosynthesized β-glucan chains and cause them to crystallize with a higher crystallinity of the metastable Iα phase, as is the case for crystallization occurring during the drawing of polymer gels.

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The limited penetration of wood by light explains why the weathering of wood exposed outdoors is a surface phenomenon. Wood is rapidly degraded by short-wavelength UV radiation, but the penetration of light into wood is positively correlated with its wavelength. Hence, subsurface degradation is likely to be caused by longerwavelength light that still has sufficient energy to degrade wood. In this paper we test this hypothesis and determine the wavelengths of visible light that extend photodegradation into wood beyond the zone affected by UV radiation. Sugi (Cryptomeria japonica) earlywood was exposed to UV and visible light with narrow band gaps (20 nm) and the penetration of light into the wood was measured using a photodetector. Photodegradation was depth-profiled using FT-IR microscopy. There was a positive correlation between the penetration of light into sugi earlywood and the wavelength of the incident radiation within the range 246-496 nm. The depth of photodegradation also increased with wavelength up to and including the violet region (403 nm) of the visible spectrum. Blue light (434-496 nm) penetrated wood to a greater extent than violet light and was capable of bleaching the wood, but it did not significantly modify lignin, and hence it was not responsible for sub-surface photodegradation of wood. We conclude that violet light is the component of the visible spectrum that extends photodegradation into wood beyond the zone affected by UV radiation. Accordingly, surface treatments designed to protect wood used outdoors should shield wood from the effects of violet light.

Computer simulations with molecular dynamics technique were carried out to investigate properties of liquid–vapor interface of methanol for a wide temperature range of 160–350 K. The estimated surface excess thermodynamic quantities, especially surface entropy, are characteristic of strongly hydrogen-bonding liquids, but the density profile resembles that of simple fluids. Orientational structuring near the surface was also studied, and one apparent tendency, much stronger than that of water, was observed; the methanol molecule projects its methyl group toward the vapor phase. This orientational ordering can be understood as a result of putting a hydrophobic methyl group outside of liquid phase to maximize the number of hydrogen bonds near the surface for energetical stabilization. A considerable part of the thermodynamic anomaly is due to this orientational ordering. Since the electric dipole is almost parallel to the surface in this orientation, the calculated surface potential is quite small, about −30 mV at room temperature.

Spin contamination errors of a broken-symmetry (BS) method in optimized structural parameters of the singlet methylene ((1)A(1)) molecule are quantitatively estimated for the Hartree-Fock (HF) method, post-HF methods (CID, CCD, MP2, MP3, MP4(SDQ)), and a hybrid DFT (B3LYP) method. For the purpose, the optimized geometry by the BS method is compared with that of an approximate spin projection (AP) method. The difference between the BS and the AP methods is about 10-20 degrees in the HCH angle. In order to examine the basis set dependency of the spin contamination error, calculated results by STO-3G, 6-31G*, and 6-311++G** are compared. The error depends on the basis sets, but the tendencies of each method are classified into two types. Calculated energy splitting values between the triplet and the singlet states (ST gap) indicate that the contamination of the stable triplet state makes the BS singlet solution stable and the ST gap becomes small. The energy order of the spin contamination error in the ST gap is estimated to be 10(-1) eV.