Abstract: Catalytic methods for the production of carbon nanotubules have been developed based on the decomposition of acetylene on well-dispersed metal particles strongly adsorbed on a support. Cobalt on silica was found to be the best catalyst-support combination for the production of graphitic tubules. The method for the catalyst preparation and the reaction conditions were optimized. Straight and coiled carbon tubules were obtained with inner and outer diameter of 3-7 and 15-20 nm, respectively, and up to 30 mum in length. These nanotubules were not coated by amorphous carbon. Traces of amorphous carbon could be removed by hydrogen. High resolution electron microscopy images and electron diffraction patterns of the straight nanotubules were similar to those obtained by the arc-discharge method. Coiled nanotubules were revealed by TEM to be regular polygonized helices where the bends are caused by pairs of pentagon-heptagon carbon rings among the hexagonal network.

Abstract: The quartic force field of thioformaldehyde has been calculated ab initio using large basis sets and augmented coupled cluster methods. Calculated fundamentals are in excellent agreement with experiment, as is the most important Coriolis coupling constant. Computed values for the anharmonicity, rovibrational coupling, and centrifugal distortion constants of the four isotopomers (H2CS)-S-32, (H2CS)-S-34, (HDCS)-S-32, and (D2CS)-S-32 have been reported. Predictions have been made for all vibrational transitions from the ground state to excited states with at most two quanta for these isotopomers, both using second-order perturbation theory corrected for Darling-Dennison resonance and using vibrational SCF-CI calculations. For (D2CS)-S-32, perturbation theory performs quite well; for the other isotopomers, performance is poorer for states involving excitation of the out-of-plane bend and, for the (H2CS)-S-32 and (H2CS)-S-34 isotopomers, also for the antisymmetric bend that is in severe Coriolis resonance with it. A possible explanation has been suggested. (C) 1994 Academic Press, Inc.

Abstract: Laser induced phase transition from b.c.c.(alpha) to f.c.c.(gamma) iron thin films is studied by high resolution TEM. The iron film has been covered on both sides with carbon layers to protect it against oxidation. Single pulse, tau FWHM = 20ns KrF (lambda = 248nm) excimer laser irradiation was performed in air with the film on the substrate. The laser pulse acts like a heat pulse followed by a rapid quenching revealing sequential aspects of the phase transition process. The presence of a fine mixture of the alpha + gamma phases between the alpha and gamma regions of the film has been interpreted as an incomplet transformation. The results are explained by assuming that the transformation took place via a phonon drag mechanism.