Vibrational dynamics of large clusters from helium atom scattering: Calculations for Ar55

Schröder, T.; Schinke, Reinhard; Krohne, R.; Buck, U.

doi:10.1063/1.474011

Cited by 13 publications

(10 citation statements)

References 22 publications

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“…In both deflection functions, the scattering angle at bϭ0 is much smaller than 180°. This is a well-known effect, which was observed previously, 5,30 and originates from the roughness of the cluster surface that scatters the helium atoms in a distribution of directions. The interaction time is almost constant for small impact parameters, rises to a maximum, and then falls off to zero when the helium atom does not hit the cluster directly anymore.…”

Section: Vibrational Excitationsupporting

confidence: 53%

“…3 By observing the inelastic energy exchange of helium atoms scattered from argon clusters in the size range of ͗n͘ϭ22-4500, we were able to demonstrate that mainly surface modes and their overtones were excited. 4,5 The transferred energy decreases from about 6 meV to 2 meV with increasing cluster size at collision energies of 25 meV and converges to the surface Rayleigh mode of solid argon. 4 Similar experiments have been carried out for water clusters of the average sizes ͗n͘ ϭ11, 22, 80, and 194 ͑Refs.…”

Section: Introductionmentioning

confidence: 92%

“…In the detailed analysis of the scattering of argon clusters from helium atoms we found that single quantum excitations are better treated quantum mechanically, while multiphonon excitations were reproduced quite well using classical trajectories. 5 The reason for the partial failure of the classical calculations has to do with the boxing problem that allocates intensity below the smallest allowed transition frequency, so that the distinction between elastic and inelastic events becomes rather vague. On the other hand is the quantum mechanical treatment of a huge number of vibrational modes, as they occur for sizes up to nϭ1000, by no means straightforward.…”

Section: Introductionmentioning

confidence: 99%

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Intermolecular vibrations of large ammonia clusters from helium atom scattering

Beu¹,

Steinbach²,

Buck³

2002

The Journal of Chemical Physics

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The excitation of the low-energy intermolecular modes of ammonia clusters by helium atom scattering has been calculated using classical trajectories. The energy transfer is investigated as a function of scattering angle ͑from 10°to 90°͒, collision energy ͑94.8 and 50.5 meV͒, cluster size (nϭ18, 100, 1000͒, and cluster temperature (T c ϭ1 K, 30-50 K, and 105 K͒. It is observed that predominantly the mode at 7 meV and to a lesser extent also the one at 12 meV are excited. These are surface modes that mainly originate from the angular motion of three adjacent N atoms. The excitation is nearly independent of the cluster size and the probability for multiphonon excitation steadily increases with increasing deflection angle. This trend is even strengthened by increasing the collision energy. The role of the cluster temperature is to broaden the energy transfer distribution with increasing values. The calculations are compared with previous and new measurements presented here of the double-differential cross sections (d/d) ⌬E of ammonia clusters of average size ͗n͘ϭ92 at two collision energies and ͗n͘ϭ1040 at one energy. While the general trends in the angular and energy dependence could be well reproduced, the correct cluster temperature was crucial in getting good agreement at the lower collision energy for nϭ100. At the higher collision energy, the large energy transfer is not reproduced, probably a shortcoming of the potential models to account correctly for the anharmonicity of the strong multiquantum excitations.

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Section: Vibrational Excitationsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Intermolecular vibrations of large ammonia clusters from helium atom scattering

Beu¹,

Steinbach²,

Buck³

2002

The Journal of Chemical Physics

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“…In fact, we were able to demonstrate that in helium atom -argon cluster collisions surface modes were predominantly excited [2]. One can distinguish between single phonon and multiphonon excitation [3] using the measured angular dependence, in conjunction with calculations. Here the method is applied to the investigation of vibrational surface properties of water particles.…”

Section: Surface Vibrations Of Large Water Clusters By He Atom Scattementioning

confidence: 92%

“…Up to now, such calculations have only been performed for the scattering of He from Ar n clusters [3,14]. The results clearly demonstrated that quasiclassical trajectories are not sufficient to describe correctly the energy transfer of single phonon excitations.…”

Section: Surface Vibrations Of Large Water Clusters By He Atom Scattementioning

confidence: 96%

Surface Vibrations of Large Water Clusters by He Atom Scattering

Brudermann¹,

Lohbrandt²,

Buck³

et al. 1998

Phys. Rev. Lett.

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The low energy intermolecular vibrational modes of water clusters for the average size n 110 have been measured by high resolution inelastic helium atom scattering. The water clusters are generated in adiabatic expansions through conical nozzles. By accompanying quantum and classical calculations the excited mode at 5.0 meV has been identified as O? ?O? ?O bending motion between adjacent hydrogen bonds, involving 3-coordinated water molecules on the amorphous cluster surface. Experiments for different sizes show that the frequency and thus the force constant of this mode increase for larger cluster sizes. [S0031-9007 (98)05739-1] PACS numbers: 36.40.Sx, 34.50.Dy, 68.35.JaWeakly bonded clusters have been a focus of intense interest during the past few years. One of the major objectives is to understand how the particles evolve as a function of size towards condensed phase behavior. The evolution of particle properties is influenced strongly by the large surface-to-bulk ratio, and therefore experimental tools sensitive specifically to the cluster surface properties are of interest. A unique tool of this kind has been developed in our laboratory, which probes surface vibrations by inelastic energy exchange with He atoms scattered from the particles [1]. In fact, we were able to demonstrate that in helium atom -argon cluster collisions surface modes were predominantly excited [2]. One can distinguish between single phonon and multiphonon excitation [3] using the measured angular dependence, in conjunction with calculations. Here the method is applied to the investigation of vibrational surface properties of water particles. Water clusters are of particular interest because of the importance of water in terrestrial phenomena, and because of the role of icy particles in atmospheric and extraterrestrial physics and chemistry. Electron diffraction studies of ͑H 2 O͒ n up to sizes of several hundred molecules demonstrated a noncrystalline structure [4], while spectroscopic studies of ice nanocrystal surfaces and surface-adsorbate systems showed persistence of amorphous surface structure to larger sizes, for which the particle interior is crystalline [5]. Thus, past studies indicate the properties of small ice particles that are quite distinct from those of bulk ice, and surface properties that are distinct from the interior. The present study focuses on these aspects of cluster behavior, for low energy, hydrogen bond vibration frequencies.For bulk hexagonal ice these modes have been measured by neutron scattering. In the range from 2 to 40 meV the peaks are attributed to the hindered intermolecular motion and interpreted as acoustical (7.1 meV) and optical (28.4 and 37.9 meV) modes [6], the splitting between the latter ones still being a subject of controversy [6,7]. The modes near 7.1 meV have also been interpreted as O? ?O? ?O bending between adjacent hydrogen bonds [8], while the higher frequency modes have been assigned to hydrogen bond stretching [6,8]. For clusters, extensive calculations are available for some sele...

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The Role of Molecular Beams in the 20th Century

Pauly¹

2000

Springer Series on Atomic, Optical, and Plasma Physics

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Vibrational dynamics of large clusters from helium atom scattering: Calculations for Ar55

Cited by 13 publications

References 22 publications

Intermolecular vibrations of large ammonia clusters from helium atom scattering

Intermolecular vibrations of large ammonia clusters from helium atom scattering

Surface Vibrations of Large Water Clusters by He Atom Scattering

The Role of Molecular Beams in the 20th Century

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