Vibrational dynamics of large clusters from high resolution He atom scattering

Buck, U.; Krohne, R.; Siebers, J.

doi:10.1007/3-540-55625-7_19

Cited by 2 publications

(4 citation statements)

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“…The measured angular distributions of the present He scattering experiments contain information on the cluster size exploiting the diffraction oscillations. The evaluation of these data gave also deviations from the scaling laws [3]. Before this point is completely clarified, we will use the scaling laws for assigning a cluster size to our experimental values which essentially reflect the source conditions for their production.…”

Section: Methodsmentioning

confidence: 98%

See 1 more Smart Citation

Diffraction and vibrational dynamics of large clusters from He atom scattering

Buck¹,

Krohne²,

Siebers³

1993

Z Phys D - Atoms, Molecules and Clusters

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Abstract. The vibrational dynamics of large Arn clusters from n=30 to n=4500 is investigated by measuring the energy loss of He atoms in a high resolution scattering experiment. The clusters are generated by adiabatic expansion through conical nozzles and contain a distribution of cluster sizes. The He supersonic nozzle beam provides a resolution of better than 1 meV. The results are compared with calculated spectral density functions for single cluster sizes and bulk phonon spectra. PACS: 36.40+dvery interesting surface properties [2]. In the present paper we report first measurements of He atom scattering from large Arn clusters in the range from n = 30 to 4500. There are mainly two different types of observables: (1) The angular distributions, which contain among other things information about the geometry and the size of the investigated objects through the diffraction oscillations. (2) The inelastic energy transfer, which is related to the excitation of the vibrational modes and which is measured by time-of-flight analysis of the scattered He atom. In this contribution we will mainly concentrate on the latter one. A preliminary account of the results appeared in [3]. I n t r o d u c t i o nThe knowledge of the frequency spectrum of a cluster plays an important role both for the interpretation of static and structural properties as well as for the dynamical behavior. This includes such quantities as the thermal free energy and the specific heat, the melting and condensation processes, and the excitation or deexcitation of the vibrational modes [1]. The latter process is of special interest, since it is very sensitive to the transition of the cluster from the discrete spectrum of vibrational modes of the molecular system to the lattice vibrations and the continuous phonon dispersion curves of the solid. The theoretical methods to study these topics reach from the classical normal mode analysis over molecular dynamics simulations to complete quantum calculations of the lattice dynamics. The experimental methods include IR-and Raman-spectroscopy for the molecular systems and neutron, electron or He atom scattering for probing bulk and surface phonons, respectively. From all these methods the scattering of He atoms appears to be the most general process to study the vibrational spectra of clusters, since this method is mainly sensitive to surface properties and obeys nearly no selection rules. In the last 10 years it has been developed into a very successful and reliable method for measuring surface phonons of the solid and for deriving a series of ExperimentalThe experiments have been carried out in a crossed molecular beam machine which is described elsewhere [4]. Essentially it consists of a He supersonic nozzle beam and a cluster beam for the target which intersect at an angle of 90 °, and a detector with an electronbombardment ionizer and a quadrupole mass filter operating under ultrahigh vacuum conditions. The angular dependence is measured by rotating the source assembly relative to the fixed detector posi...

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Section: Methodsmentioning

confidence: 98%

“…In this contribution we will mainly concentrate on the latter one. A preliminary account of the results appeared in [3].…”

Section: Pacs: 3640+dmentioning

confidence: 95%

Diffraction and vibrational dynamics of large clusters from He atom scattering

Buck¹,

Krohne²,

Siebers³

1993

Z Phys D - Atoms, Molecules and Clusters

View full text Add to dashboard Cite

show abstract

“…In these cases the vibrational spectrum is obtained by the Fourier transform of the velocity autocorrelation function. 4,5,7,8,13,16 These studies are not very well suited to get answers in a systematic way. A better approach for deriving this information on many sizes is the so-called dense sphere model which is based on elastic continuum mechanics of solid material.…”

Section: The Dense Sphere Modelmentioning

confidence: 99%

“…This can be easily visualized by looking at the calculated spectra of different Ar n clusters as a function of size. [4][5][6][7][8] Small clusters such as Ar 13 ͑Ar 19 ) exhibit a series of lines around 3 meV which represent the motion of the surface atoms and a single line around 7.5 meV which correspond to the interior at-om͑s͒ in a bulklike environment. This trend continues for the larger clusters and goes over into the behavior of the bulk solid which shows intensity peaks at 5 and 8 meV.…”

Section: Introductionmentioning

confidence: 99%