Kazuo Takeuchi

Bio: Kazuo Takeuchi is an academic researcher from Saitama University. The author has contributed to research in topics: Isotope separation & Dissociation (chemistry). The author has an hindex of 21, co-authored 215 publications receiving 1831 citations. Previous affiliations of Kazuo Takeuchi include Osaka University & Hitachi.

XPS study of a photopolymerized C 60 film

Abstract: The changes in the valence band and the C 1s core peak and its shake-up satellite of a ${\mathrm{C}}_{60}$ film upon photopolymerization are studied by x-ray photoelectron spectroscopy. It was found that the intensity of the C 1s shake-up satellite of the phototransformed ${\mathrm{C}}_{60}$ film decreased with increasing irradiation time of a 500-W mercury lamp (0--200 h). On the other hand, the valence-band structure of the ${\mathrm{C}}_{60}$ film was almost unchanged even after 200 h of irradiation, compared with that of the pristine ${\mathrm{C}}_{60}$ film. This suggests that the change in the transition probability of each C 1s shake-up satellite peak (\ensuremath{\pi}-\ensuremath{\pi} transitions) is very small after irradiation and thus plays only a minor role in the reduction of the satellite intensity. The average number of [2+2] cycloadditional four-membered ring structures on a ${\mathrm{C}}_{60}$ molecule was estimated from the decrease in the satellite intensity.

Vibrational modes and IR analysis of neutral photopolymerized C 60 dimers

Abstract: Motivated by recent experiments on ${\mathrm{C}}_{60}$ dimers, we have performed total-energy minimizations for several isomers of the ${\mathrm{C}}_{60}$ dimer in the neutral configuration in order to find the ground-state structure. The phonon spectra and electronic energy levels have also been calculated within the generalized tight-binding approximation. From these calculations, one can also deduce the IR absorption spectrum. By comparing our results with the available IR experimental data, we can draw conclusions regarding the structure of the ${\mathrm{C}}_{60}$ dimer used in the experiments.

CO2 laser tritium isotope separation: Collisional effects in multiphoton dissociation of trifluoromethane

Abstract: Multiphoton dissociation of ppm level CTF3 in CHF3 is reported. The effect of buffer gas pressure on the specific dissociation rates and the isotopic selectivity is investigated. Pulse energy dependence of the dissociation rates is converted to the intrinsic relation between the fractional conversion per pulse and the fluence by means of the new deconvolution technique. By addition of 100 Torr argon, the critical fluence of CTF3 was decreased from 136 to 34 J/cm2, while the intrinsic selectivity was increased from 34 to 580. In the absence of buffer gas argon, the fractional conversion per pulse exhibits two different pressure dependences. Unlike in the case below 15 Torr, the system shows strong pressure dependence and loss of the isotopic selectivity above 15 Torr. Possible application to the tritium removal process is also discussed.

In situ high-resolution infrared spectroscopy of a photopolymerized C 60 film

Abstract: Photopolymerized ${\mathrm{C}}_{60}$ film has been studied under a water-vapor-free condition by means of in situ high-resolution (0.25 ${\mathrm{cm}}^{\ensuremath{-}1}$) Fourier-transform infrared (FT-IR) spectroscopy. It was found that the IR spectrum of a pristine ${\mathrm{C}}_{60}$ film changed markedly after 10-h irradiation with a 500 W mercury lamp at a CsI substrate temperature of 27 \ifmmode^\circ\else\textdegree\fi{}C, whereas no change in the IR spectrum of the ${\mathrm{C}}_{60}$ film was observed after 20-h irradiation with the lamp at a substrate temperature of 100 \ifmmode^\circ\else\textdegree\fi{}C. Compared with the previous FT-IR result reported by Rao et al. [Science 259, 955 (1993)], the present IR spectra for the photopolymerized film had many new peaks and the peaks corresponding to the four intrinsic intensive IR-active modes were split. A ${\mathrm{C}}_{60}$ dimer structure is postulated after comparison between the present results and the theoretical IR calculations reported by Adams et al. [Phys. Rev. B 50, 17 471 (1994)] and Pederson and Quong [Phys. Rev. Lett. 74, 2319 (1995)].

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Controlling molecular deposition and layer structure with supramolecular surface assemblies

Abstract: Selective non-covalent interactions have been widely exploited in solution-based chemistry to direct the assembly of molecules into nanometre-sized functional structures such as capsules, switches and prototype machines1,2,3,4,5. More recently, the concepts of supramolecular organization have also been applied to two-dimensional assemblies on surfaces6,7 stabilized by hydrogen bonding8,9,10,11,12,13,14, dipolar coupling15,16,17 or metal co-ordination18. Structures realized to date include isolated rows8,13,14,15, clusters9,10,18 and extended networks10,11,12,17, as well as more complex multi-component arrangements16. Another approach to controlling surface structures uses adsorbed molecular monolayers to create preferential binding sites that accommodate individual target molecules19,20. Here we combine these approaches, by using hydrogen bonding to guide the assembly of two types of molecules into a two-dimensional open honeycomb network that then controls and templates new surface phases formed by subsequently deposited fullerene molecules. We find that the open network acts as a two-dimensional array of large pores of sufficient capacity to accommodate several large guest molecules, with the network itself also serving as a template for the formation of a fullerene layer.

Detection and characterization of engineered nanoparticles in food and the environment

Abstract: Nanotechnology is developing rapidly and, in the future, it is expected that increasingly more products will contain some sort of nanomaterial. However, to date, little is known about the occurrence, fate and toxicity of nanoparticles. The limitations in our knowledge are partly due to the lack of methodology for the detection and characterisation of engineered nanoparticles in complex matrices, i.e. water, soil or food. This review provides an overview of the characteristics of nanoparticles that could affect their behaviour and toxicity, as well as techniques available for their determination. Important properties include size, shape, surface properties, aggregation state, solubility, structure and chemical composition. Methods have been developed for natural or engineered nanomaterials in simple matrices, which could be optimized to provide the necessary information, including microscopy, chromatography, spectroscopy, centrifugation, as well as filtration and related techniques. A combination of these is often required. A number of challenges will arise when analysing environmental and food materials, including extraction challenges, the presence of analytical artifacts caused by sample preparation, problems of distinction between natural and engineered nanoparticles and lack of reference materials. Future work should focus on addressing these challenges.

Nanoparticles and the Environment

Abstract: Nanoparticles are a class of materials with properties distinctively different from their bulk and molecular counterparts. A critical review of the very broad topic of environmental nanoparticles is presented. Because of the vast nature of the topic, the review is focused primarily on gas-borne nanoparticles. The "life history of nanoparticles" is presented, tracking it from its formation to its potential use and eventual fate in the environment. Nanoparticle sources, anthropogenic emissions from industrial and occupational settings, and conversion and formation in the atmosphere are discussed. The ability to characterize and capture these nanoparticles (as would be necessary in a nanoparticle production system), as well as their control (of emissions from an industrial source) is discussed. A description on the use of nanoparticles in environmental technologies and the potential impact on the energy sector is provided. The potential effects on human health and the environment, both adverse and beneficial, are important aspects that need to be considered. As will be evident, the study of "environmental nanoparticles" is a new and fast-growing field. Much work remains to be done before we can fully harness the advantages of nanoparticles and ensure that there are no potential adverse consequences. A set of recommendations for additional work in each area is provided.