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Papers by Arthur Vayloyan

ABSTRACT Diss. Naturwiss. Bern (kein Austausch).

Physics and Chemistry of Small Clusters, 1987

Extensive measurements of ionisation potentials and relative thermodynamic stabilities for pure a... more Extensive measurements of ionisation potentials and relative thermodynamic stabilities for pure alkali and alkali/heteroatom species have provided much data pertinent to the electronic structure of simple metal clusters. Due to poorly characterised internal temperatures, an understanding of the relative magnitude of electronic versus geometric structure effects remains tenuous. Particle specific studies of chemical reactivity are ongoing.

Review of Scientific Instruments, 1997

ABSTRACT A new thermal, supersonic cluster source for the investigation of binary metal cluster f... more ABSTRACT A new thermal, supersonic cluster source for the investigation of binary metal cluster formation at thermodynamically well-defined expansion conditions is described. The source consists of two separately heatable cartridges. A first cartridge can be heated up to 1220 K and the second high temperature cartridge reaches maximal temperatures of 1800 K. A temperature difference of 1000 K between the two cartridges can be maintained for at least 3 h. Clustering occurs upon supersonic expansion from a conical nozzle. This cluster source has two main applications: (a) the generation of mixed metal clusters and (b) the investigation of pure metal clusters at various expansion conditions. The performance and applications of this source are illustrated by presenting results of the heterocluster formation of mixed sodium/gold and sodium/silver heteroexpansions. In addition, the influence of the oven parameters on the internal temperatures of the generated clusters is illustrated with the example of Na2. © 1997 American Institute of Physics.

The Journal of Chemical Physics, 1996

One of the goals of cluster science is to identify unifying concepts of matter at the molecular a... more One of the goals of cluster science is to identify unifying concepts of matter at the molecular and the bulk limit. One hopes that the microscopic approach to understand macroscopic phenomena will help separating local from collective contributions to properties of bulk ...

Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1987

Fragmentation of sodium cluster ions (Na~ + , x <42) was studied via photoionisation of neutral p... more Fragmentation of sodium cluster ions (Na~ + , x <42) was studied via photoionisation of neutral precursors, Expansions of metal vapor out of cylindrical and conical nozzles yielded supersonic beams with differing cluster compositions. Measurements of photoionisation efficiency curves in the 3-6 eV range for both types of expansion allow quantitative separation of direct ionisation and unimolecular dissociation contributions to specific ion signals. Data for Na~ and Na~-are analysed to yield lower limits on bond energies. Results obtained for larger clusters are also discussed.

Israel Journal of Chemistry, 1990

Mixed metal clusters of sodium with copper, silver, and gold were produced by supersonic expansio... more Mixed metal clusters of sodium with copper, silver, and gold were produced by supersonic expansions at well-defined thermodynamic conditions. Differences in the behavior toward binary alloying, cluster formation, and relative thermodynamic stabilities are discussed within a structureless, delocalized, electronic shell model and using molecular orbital arguments and the different strengths of the relativistic effects of the coinage metals. Free-energy changes (∆G) of selected exchange reactions are determined, showing the substitution of gold atoms to be thermodynamically the most favored. This is due to the preferred s-d hybridization in gold atoms, leading to a stronger metal-metal interaction. The measured ionization potentials reveal a distinct shell closing at the octamer for all three heterosystems. The drop of the ionization potential going from the octamer to the nonamer is most pronounced for the sodium-silver heteroclusters and is almost as large as for pure sodium clusters.

ABSTRACT Diss. Naturwiss. Bern (kein Austausch).

Physics and Chemistry of Small Clusters, 1987

Extensive measurements of ionisation potentials and relative thermodynamic stabilities for pure a... more Extensive measurements of ionisation potentials and relative thermodynamic stabilities for pure alkali and alkali/heteroatom species have provided much data pertinent to the electronic structure of simple metal clusters. Due to poorly characterised internal temperatures, an understanding of the relative magnitude of electronic versus geometric structure effects remains tenuous. Particle specific studies of chemical reactivity are ongoing.

Review of Scientific Instruments, 1997

ABSTRACT A new thermal, supersonic cluster source for the investigation of binary metal cluster f... more ABSTRACT A new thermal, supersonic cluster source for the investigation of binary metal cluster formation at thermodynamically well-defined expansion conditions is described. The source consists of two separately heatable cartridges. A first cartridge can be heated up to 1220 K and the second high temperature cartridge reaches maximal temperatures of 1800 K. A temperature difference of 1000 K between the two cartridges can be maintained for at least 3 h. Clustering occurs upon supersonic expansion from a conical nozzle. This cluster source has two main applications: (a) the generation of mixed metal clusters and (b) the investigation of pure metal clusters at various expansion conditions. The performance and applications of this source are illustrated by presenting results of the heterocluster formation of mixed sodium/gold and sodium/silver heteroexpansions. In addition, the influence of the oven parameters on the internal temperatures of the generated clusters is illustrated with the example of Na2. © 1997 American Institute of Physics.

The Journal of Chemical Physics, 1996

One of the goals of cluster science is to identify unifying concepts of matter at the molecular a... more One of the goals of cluster science is to identify unifying concepts of matter at the molecular and the bulk limit. One hopes that the microscopic approach to understand macroscopic phenomena will help separating local from collective contributions to properties of bulk ...

Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1987

Fragmentation of sodium cluster ions (Na~ + , x <42) was studied via photoionisation of neutral p... more Fragmentation of sodium cluster ions (Na~ + , x <42) was studied via photoionisation of neutral precursors, Expansions of metal vapor out of cylindrical and conical nozzles yielded supersonic beams with differing cluster compositions. Measurements of photoionisation efficiency curves in the 3-6 eV range for both types of expansion allow quantitative separation of direct ionisation and unimolecular dissociation contributions to specific ion signals. Data for Na~ and Na~-are analysed to yield lower limits on bond energies. Results obtained for larger clusters are also discussed.

Israel Journal of Chemistry, 1990

Mixed metal clusters of sodium with copper, silver, and gold were produced by supersonic expansio... more Mixed metal clusters of sodium with copper, silver, and gold were produced by supersonic expansions at well-defined thermodynamic conditions. Differences in the behavior toward binary alloying, cluster formation, and relative thermodynamic stabilities are discussed within a structureless, delocalized, electronic shell model and using molecular orbital arguments and the different strengths of the relativistic effects of the coinage metals. Free-energy changes (∆G) of selected exchange reactions are determined, showing the substitution of gold atoms to be thermodynamically the most favored. This is due to the preferred s-d hybridization in gold atoms, leading to a stronger metal-metal interaction. The measured ionization potentials reveal a distinct shell closing at the octamer for all three heterosystems. The drop of the ionization potential going from the octamer to the nonamer is most pronounced for the sodium-silver heteroclusters and is almost as large as for pure sodium clusters.