112 research outputs found
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 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 , 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
SPECTROSCOPY OF AND MOLECULES IN NEON AND ARGON MATRICES
B. Kleman, Astrophys, J. 125, 162 (1956). L. Gausset, G. Herzberg, A. Lagerquist and B. Rosen, Faraday Society (in press)Author Institution: Union Carbide Research Institute“The spectrum of the molecule trapped in neon and argon matrices at and has been studied in absorption in the infrared and near-ultravoilet regions and in fluorescence in the visible region. Many features of the well-known cometary emission spectrum beginning at 4050\AA and strikingly reproduced in the neon absorption spectrum. substitution has also been used to prove that is isolated is isolated under the extreme conditions prevailing during the preparation of the matrices. Analysis of the near-ultraviolet bands yields the excited-state frequencies: . Fluorescence and infrared measurements give the ground-state frequencies: . Our ultraviolet spectra are in accord with the low bending frequency, , recently proposed by Gausset, Herzberg, Lagerquist, and Other complexities in the spectrum indicate that the observed transition may be - rather than the expected . A similar study has been made of the molecule which has been observed in stellar spectra and produced in the laboratory by . The matrices have been prepared by trapping the vapour effused from hot silicon carbide. The absorption spectrum in a neon matrix begins at 4963{\AA} (as compared to 4977{\AA} in the gas) and contains some weak bands not observed by Kleman. The matrix may also exhibit the spectra of the , and molecules, depending upon the conditions of vaporization.
SPECTROSCOPY OF TRANSITION-METAL OXIDE MOLECULES IN RARE-GAS MATRICES AT AND .
Author Institution: Union Carbide Research InstituteThe infrared, visible, and near-ultraviolet spectra of TiO, ZrO, HfO, WO, (and ) have been observed in neon and argon matrices at and with and substitution. A discussion will be given of the spectra and the molecular orbitals and ground states of the diatomic and triatomic molecules. The larger tungsten oxide molecules have been observed in the infrared only; the particular trapped species varying with the conditions of vaporization. It is found that (1) the spectra confirm a ground state for (2) ZrO, and probably HfO, have a ground state, (3) the electronic spectra exhibit many vibrational perturbations not present in the spectra, (4) the spectra are like those of , so that is bent in the ground and excited (5) each of the numerous infrared bands of the molecules can usually be assigned to particular species with the help of mass spectrometric J. G. Phillips, Astrophys, J. 115, 567 (1962). W. Weltner, Jr. and D. McLeod, Jr., J. Chem. Phys. 42, 882 (1965). J. Berkowitz, W. A. Chupka, M. G. Inghram, J. Chem. Phys. 27, 85 (1957); R. J. Ackermann and E. G. Rauh, J. Phys. Chem. 67, 2596 (1963)
ESR OF THE BO AND AlO MOLECULES: EVIDENCE FOR A AlO Kr MOLECULE AT
L. B. Knight, JR., W. C. Easley, and W. Weltner, JR., J. Chem. Phys. 52 1607 (1970).""Author Institution: Department of Chemistry, University of FloridaBO and AlO molecules have been trapped in rare-gas matrices at in their ground states. Hyperfine (hf) interactions, g tensor, and matrix effects are strikingly different for these two species. BO exhibits a large unpaired spin density at the boron nucleus, is highly oriented in a ncon matrix, and has g values near in all matrices. In the ionic AlO molecule, only 20% of the odd electron is on the aluminum atom, and and (hf splitting of ) are extremely sensitive to the rare-gas hf structure has been resolved in that matrix associated with an extra set of lines that vanish above and reappear upon cooling to . The molecule formed between AlO and one Kr atom is presumably linear and exhibits a high degree of preferential orientation in the matrix. Its Al hfs is greater than that of AlO in a non-complexed lattice site
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