An improved clusterion-photoelectron coincidence technique for the investigation of the ionisation dynamics of clusters

Abstract.A minimum-basis diatomics-in-molecules (DIM) model previously developed for singly-ionized argon clusters is applied to neon clusters, Ne + , for n = 3, 4,...,22. A search for the global minimum energy of each cluster yields structures with the positive charge localised on a dimer-ion. This appears to be due largely to the linear unsymmetrical configuration which the model finds for Ne~-. For this reason, the structures of the clusters at their minimum energy are different from those for Ar, + computed with the same model. On the other hand, the behaviour of the charge distribution as a function of the geometrical configuration is similar to that for Ar + , as are the overall shapes of the potential energy surfaces. The results are discussed in terms of the charge distributions and the ratios of equilibrium properties of the dimers and dimer-ions which constitute the input to the model.

Section: Introductionmentioning

confidence: 99%

A diatomics-in-molecules model for singly ionized neon clusters

Fieber

Ding

Kuntz

1992

“…The combined processes lead to the above mentioned special abundances in the mass spectra, the magic (or antimagic) numbers for which mostly the specific stabilities of the ion clusters are thought to be responsible. A variety of experimen-tal studies on unimolecular, collision and photon induced rare gas cluster fragmentation [19][20][21][22][23][24][25][26][27][28][29][30] gives evidence for these concepts as well as theoretical simulations of cluster dynamics [31][32][33]. The crucial crossed beam experiments of Buck and Meyer [34][35][36] gave direct evidence of this fragmentation after electron impact ionisation (with some 100 eV electron kinetic energy) and showed quantitatively that over 95% of At, clusters with n up to 6 fragmented into monomer or dimer ions.…”

Section: Introductionmentioning

confidence: 99%

Photoionisation studies of homogeneous argon and krypton clusters using TPEPICO

Kamke

Vries

Krauss

et al. 1989

The photoionisation threshold region of homogeneous Argon and Krypton clusters Ar, and Kr, for n up to 24 formed in a free jet expansion has been studied in detail, using the threshold photoelectron photoion coincidence (TPEPICO) time of flight technique. Measurements performed at a variety of different expansion conditions (nozzle temperature and stagnation pressure) demonstrate that fragmentation of larger clusters contributes substantially to the shape of the TPEPICO spectra even for the smallest clusters and at all photon energies higher than about 200 meV to 400 meV above the ionisation threshold. The determination of ionisation potentials for these cluster ions is discussed and careful estimates are given and compared with recent theoretical values.

“…The experiments were performed in a two chamber molecular beam apparatus which has been described in principle in an earlier publication [15]. It is shown schematically in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore we have applied the TEPICO (Threshold Electron Photo Ion COincidence) method [14,15] to this type of cluster experiment: The mass spectra of the cluster ions are measured using a time of flight technique in coincidence with the electrons which have kinetic energies of approximately zero. By being limited to zero energy electrons not all processes will be detected and so only a selected number of systems can be analyzed: this can be done, however, in much greater detail compared with other conventional methods.…”

Section: Introductionmentioning

confidence: 99%

Fragmentation spectroscopy of heterogeneous clusters

Holub-Krappe¹,

Ganteför²,

Bröker³

et al. 1988

Self Cite

Photoionisation experiments were performed with heterogeneous Ar-Xe-clusters produced by supersonic expansion of argon gas with small quantities of xenon added to it. A threshold-electron photoionisation (TEPICO) technique was used to obtain time of flight cluster mass spectra. These mass spectra show particularly strong intensities for Ar12Xe + and ArlsXe + which are attributed to the extraordinary stabilities of these cluster ions. Maxima in the ionic size distribution around ArTXe + are related to a particular abundance of neutral Ar12Xe which is fragmented after ionization. These stabilities are explained in terms of geometries consisting of a central Xe atom or ion surrounded by shells of Ar atoms. Filled shells exhibit particular strong bonding because these exhibit the largest number of atom-atom bonds. This conclusion is supported by simple theoretical calculations. The ionization process is discussed in terms of two direct and one indirect ionization channels the latter one proceeding via an intermediate electronic excitation of the Ar component in the neutral cluster.