Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

est frame of the string. The modified model can be used both for a description of different processes and for an analysis of nucleusnucleus
interactions at intermediate energies.
NTIS
Mesons; Protons; Nuclear Interactions; Transverse Momentum
20000064067 NASA Ames Research Center, Moffett Field, CA USA
Structure of Co(H2)n + Clusters, for n = 1-6
Bauschlicher, Charles W., Jr., NASA Ames Research Center, USA; Maitre, Philippe, California Univ., USA; Journal of Physical
Chemistry; 1995; ISSN 0022-3654; Volume 99, pp. 3444-3447; In English; Copyright; Avail: Issuing Activity
The geometries and H2 binding energies have been determined for Co(H2)n (sup +), for n = 1-6. The binding energies are
in good agreement with experiment. The shape of the clusters is used to explain the pairwise decrease in the binding energies. The
bonding in CoH2 (sup +) and Co(H2)2 (sup +) is very similar and is enhanced by sd (sigma) hybridization. The next two H2 molecules
add to the side of Co(H2)2 (sup +). These two additional H2 molecules cannot benefit from sd (sigma) hybridization and
are less strongly bound. The addition of the fifth and sixth H2 molecules eliminates sd (sigma) hybridization as a mechanism for
reducing Co-H2 repulsion. This coupled with the smaller Co to H2 (sigma *) donation results in another decrease in the binding
energies.
Author
Hydrogen; Cobalt; Chemical Bonds; Molecular Clusters; Hybrid Structures
20000064084 NASA Ames Research Center, Moffett Field, CA USA
Theoretical Study of Electron Scattering by Small Clusters and Adsorbates
Huo, Winifred M., NASA Ames Research Center, USA; Sheehy, J. A., Eloret Corp., USA; Electron Collisions with Molecules,
Clusters, and Surfaces; [1994], pp. 171-182; In English; Copyright; Avail: Issuing Activity
Current interest in clusters stems from their role as novel materials as well as a possible extension of cluster results to bulk
systems. Experimental investigations on clusters have been carried out using laser spectroscopy, microwave spectroscopy, heavyparticle
collisions, as well as electron collisions with earlier experimental work on electron attachment and ionization having been
reviewed previously. Recently, Mark and coworkers studied the decay channels of cluster ions following electron impact ionization.
Rauth et al. reported the formation of the superhalogen ion SF7(-) and other nonstoichiometric cluster ions in their study of
electron attachment to SF6 clusters. Kresin et al. measured the absolute electron-impact depletion cross section of metal clusters
Na8, Na(20), and Na(40). They found that the inelastic scattering cross section increased with cluster size and was considerably
greater than the hard sphere collision cross sections. They hypothesized that electron attachment and collision-induced fragmentation
were the dominant physical processes responsible for this effect. For the two smaller clusters, they also found a sharp increase
in the cross section near threshold. Most theoretical studies of clusters have been devoted to their electronic structures, vibrational
relaxation, and predissociation while investigations of electron scattering from clusters has been lacking. In view of this, we
recently undertook an ab initio study of electron scattering from small Be clusters and BeCO. Beryllium was chosen because it
is readily amenable to ab t’nitio calculations. Moreover, the electronic structure of Be clusters has been studied extensively, showing
that the Be-Be bond is relatively weak in comparison with a normal chemical bond. Our investigation focuses on how the cross
sections change with cluster size and geometry. The range of energy studied, 0.05 - 5.0 eV, is chosen because of the ubiquitous
resonance in the low-energy scattering of Be. Hence it can be determined if it is possible, as a consequence of the weaker bonds
in the Be clusters, to identify the atomic origin of the cluster resonance.
Derived from text
Numerical Analysis; Electron Scattering; Adsorption; Atomic Clusters; Electronic Structure; Inelastic Scattering; Ionization;
Scattering Cross Sections
20000065647 Joint Inst. for Nuclear Research, Frank Lab. of Neutron Physics, Dubna, USSR
Search for low-energy upscattering of ultracold neutrons from a beryllium surface
Muzychka, A.; Pokotilovskij, Y.; Geltenbort, P.; Dec. 31, 1998; 20p; In English
Report No.(s): DE99-607982; JINR-E-3-98-41; No Copyright; Avail: Department of Energy Information Bridge
The results are presented of the search for the anomalous low energy upscattering of ultracold neutrons from beryllium surface.
This upscatterring is considered as one of the possible reasons of UCN ’disappearance’ from very cold beryllium bottles,
observed in experiments. The Indium foil activation method was used to measure a very low intensity flux of upscattered UCN.
The (15-250) m/s velocity interval of upscattered UCN is excluded in these measurements with CL 90%.
NTIS
Inelastic Scattering; Cold Neutrons; Nuclear Physics
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