Prismane C_8: A New Form of Carbon?

Our numerical calculations on small carbon clusters point to the existence of a metastable three-dimensional eight-atom cluster C$_8$ which has a shape of a six-atom triangular prism with two excess atoms above and below its bases. We gave this cluster the name "prismane". The binding energy of the prismane equals to 5.1 eV/atom, i.e., is 0.45 eV/atom lower than the binding energy of the stable one-dimensional eight-atom cluster and 2.3 eV/atom lower than the binding energy of the bulk graphite or diamond. Molecular dynamics simulations give evidence for a rather high stability of the prismane, the activation energy for a prismane decay being about 0.8 eV. The prismane lifetime increases rapidly as the temperature decreases indicating a possibility of experimental observation of this cluster.Comment: 5 pages (revtex), 3 figures (eps

Theoretical study of the stable states of small carbon clusters Cn (n = 2-10)

Both even- and odd-numbered neutral carbon clusters Cn (n = 2-10) are systematically studied using the energy minimization method and the modified Brenner potential for the carbon-carbon interactions. Many stable configurations were found and several new isomers are predicted. For the lowest energy stable configurations we obtained their binding energies and bond lengths. We found that for n < 6 the linear isomer is the most stable one while for n > 5 the monocyclic isomer becomes the most stable. The latter was found to be regular for all studied clusters. The dependence of the binding energy for linear and cyclic clusters versus the cluster size n (n = 2-10) is found to be in good agreement with several previous calculations, in particular with ab initio calculations as well as with experimental data for n = 2-5.Comment: Submitted to Phys. Rev.

Superconductivity in Fullerides

Experimental studies of superconductivity properties of fullerides are briefly reviewed. Theoretical calculations of the electron-phonon coupling, in particular for the intramolecular phonons, are discussed extensively. The calculations are compared with coupling constants deduced from a number of different experimental techniques. It is discussed why the A_3 C_60 are not Mott-Hubbard insulators, in spite of the large Coulomb interaction. Estimates of the Coulomb pseudopotential $\mu^*$, describing the effect of the Coulomb repulsion on the superconductivity, as well as possible electronic mechanisms for the superconductivity are reviewed. The calculation of various properties within the Migdal-Eliashberg theory and attempts to go beyond this theory are described.Comment: 33 pages, latex2e, revtex using rmp style, 15 figures, submitted to Review of Modern Physics, more information at http://radix2.mpi-stuttgart.mpg.de/fullerene/fullerene.htm

Chemical composition of a concretion dredged from lake Madüsee (lake Miedwie, Poland)

This article describes the bottom sediments, lake ores and limestone bedrock dredged from lake Mad¸see in Pommerania now known as lake Miedwie in Poland

ESR of matrix isolated bromine atoms produced in the H+Br<SUB>2</SUB> reaction

The products of the H(D)+X2 reaction, where X is Br, Cl, or F, have been trapped in solid argon at 4 &#959;K and observed via ESR. With Br2 as reactant the observed spectra are attributed to Br atoms electronically quenched in an axial crystal field. The spectra obtained using the other halogens were not clearly attributable to quenched atoms. The ESR of matrix-isolated Br atoms has not been observed previously, {While this paper was being reviewed, H. Muto and L. D. Kispert observed the ESR spectrum of partially quenched Br atoms in x-irradiated N-bromosuccinimide single crystals [J. Chem. Phys. 72, 2300 (1980)]} but their magnetic properties are similar to those recently observed by Iwasaki, Toriyama, and Muto for I atoms quenched in solid xenon. For Br: g =2.646(1), g =1.55(1), A =1937(20) MHz, A =423(10) MHz, and Q =100(10) MHz. Comparison was made with crude axial crystal field predictions derived using the magnetic parameters of the gas-phase atom