B. Tribollet

Binding energy and electronic properties in antimony clusters: Comparison with bismuth clusters

Antimony clusters are produced by the gas aggregation method. They are found to be built from Sb4 units. The Sb+4n clusters are demonstrated to relax their excess energy by evaporation of a tetramer and the binding energy of Sb4 in the cluster is measured to be about 1.3 eV, well below the binding energy of a Sb atom in the bulk (≊2.75 eV). The ionization potentials of Sb4n clusters are studied as a function of the size and the observed evolution confirms the nonmetallic character of their structure. These results are compared with those obtained for bismuth clusters which exhibit a very different behavior. Finally the possible metastable character of Sb4n structure is discussed and illustrated by experiments performed as a function of inert gas temperature in the clusters source.Antimony clusters are produced by the gas aggregation method. They are found to be built from Sb4 units. The Sb+4n clusters are demonstrated to relax their excess energy by evaporation of a tetramer and the binding energy of Sb4 in the cluster is measured to be about 1.3 eV, well below the binding energy of a Sb atom in the bulk (≊2.75 eV). The ionization potentials of Sb4n clusters are studied as a function of the size and the observed evolution confirms the nonmetallic character of their structure. These results are compared with those obtained for bismuth clusters which exhibit a very different behavior. Finally the possible metastable character of Sb4n structure is discussed and illustrated by experiments performed as a function of inert gas temperature in the clusters source.

Velocity slip measurements of bismuth clusters produced by the inert gas condensation technique

The velocities of bismuth clusters produced by the inert gas condensation technique have been measured by the time of flight spectrometer. A large velocity slip has been observed between the helium carrier gas and the clusters. The translational temperature of helium has been also measured. Although the fragmentation phenomena associated with electron impact ionization precludes a precise determination of the temperature of the clusters, this temperature can be roughly estimated and our results show that a partial mass selection of neutral clusters by a velocity selector is possible.

Electronic properties and fragmentation processes for singly and doubly charged indium clusters

Indium clusters are produced by the inert gas condensation technique. The ionization potentials are found higher for small clusters than for the indium atom. This result is interpreted by the p character of the bonding as in aluminum. The fragmentation processes are studied and discussed. The behavior of the ionization potential explains why the evaporation of neutral monomers is an unlikely channel in the dissociation processes. Finally doubly charged indium clusters are detected for n≥15 and their ionization threshold is determined. Triply charged clusters are also observed.

Comparison between selenium and tellurium clusters

Selenium and tellurium clusters are produced by the inert gas condensation technique. The mass spectra of both species are completely different and reveal different properties. In selenium, a periodicity of 6–7 is observed and may be interpreted by the binding energy between small cyclic molecules. Moreover, it was very difficult to obtained large clusters probably because the binding energy between these molecules is very small. In tellurium, these periodic structures do not exist and large clusters are easily obtained in nucleation conditions where only small selenium clusters are present. These results are discussed and a simple nucleation model is used to illustrate this different behavior. Finally these clusters properties are correlated to the bulk structure of both materials.

Experimental studies on selenium cluster structures

In this paper, we report properties of selenium clusters produced by vapor condensation technique. Impact electronic ionization is performed on clusters in the size range from 2 to 36 atoms. The measured ionization potentials exhibit small oscillation corresponding to the wiggles observed on the mass distribution. An attempt to connect these experimental observations with the geometrical structure of the molecules is made in the discussion.

Study of selenium clusters. Evidence of packing structure

The aim of this paper is to study the properties of selenium clusters produced by vapor condensation technique. Simulation of nucleation process up to 50 atoms are in favour of a structure close to the amorphous structure. Doubly charged clusters are also obtained in the mass spectra.

Microwave transitions between molecular Rydberg states

Abstract Microwave transitions are observed for the first time between molecular Rydberg states in an optical—optical—microwave triple-resonance experiment carried out on Rydberg states of the Na 2 molecule. A new Rydberg series of u symmetry is observed and its quantum defect is measured (μ = 0.14). Our results demonstrate the potential of microwave transitions for study of molecular Rydberg states.

Structure of small rare earth clusters

Rare earth clusters are produced by the inert gas condensation technique. The observed size distribution shows large peaks atn=13, 19, 23, 26, 29, 32, 34, 37, 39, 45, ... The beginning of this sequence (up to 34) has been already observed in argon clusters and recently by our group in barium clusters; this sequence may be interpreted in terms of icosahedral structures corresponding to the addition of caps on a core icosahedron of 13 atoms.

State-selected ion photodissociation

Using the optical optical double resonance (O.O.D.R.) technique, Na2 molecules in a supersonic beam are ionized in well defined v J levels of the Na2 + X 2∑ u + ground state. These ions are then laser photodissociated as a function of the previously prepared vibrational level. As a result, we determine the potential curve of the first Na2 + 2Π u state. Dipole moment transition and photodissociation cross-sections are also calculated.

Photodissociation of an I2 supersonic beam in the nozzle expansion region: Influence on cluster spectra

Abstract Iodine clusters are obtained by free expansion of iodine vapour. The I2 molecule is then photodissociated by a cw laser in the nozzle expansion region. Hot dissociated 1 atoms partially prevent nucleation, allowing accurate probing of the nucleation region. Moreover, I atoms can act as germs for the formation of odd clusters I2n-1, leading to an increase of the ratio (number of I2n-1+/number of I2n+).