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Communication Dans Un Congrès Année : 2022

Modelling of ultra-cold helium nanodroplet dynamics

Résumé

For the past 30 years, helium nano-droplets have been of particular interest to experimentalists. Indeed, this is a cold dense finite liquid environment which is an excellent matrix for spectroscopy applications, in atomic and molecular collision physics as well as in ultra cold chemistry with ability of isolating interesting reactions intermediates like HOCO in OH + CO → CO2 + H or to synthesize new materials as metallic nano-wires. These phenomena are consequences of the quantum collective behaviour of helium atoms at temperature T < 1 K which classify helium nano-droplets as quantum liquids. In this thesis work we propose to model photo-dissociation [1] of immersed diatomic as molecular iodine, doping and rotational excitation of these droplets by using an home-made molecular dynamics developed by Pr. Marius Lewerenz, the CLUSTER code. To take the quantum nature of helium atoms into account the methodology exploits the quantum effective potential technique [2] at experimental work temperature 0.37 K. With the photo-dissociation, an excitation above a molecular fragmentation limit leads to two possible scenarios depending one the amortised energy by the helium droplets. The first one is the fast recombination so-called ’cage effect’ [3] and the second is where photo-fragments reside in the helium bath. But with nano-meter scale of droplets a third scenario is possible with fragments leaving the cluster surrounded by a helium solvating shell. Results are shown for helium nano-droplets containing thousands atoms (2500 to 9000 He) and statistics on size and velocity of I@Hen photo-fragments have been computed and are similar to experimental outcomes for analogous system CH3I [4]. According experiments using 1 fs X-ray flashes [5], the helium nano-droplets are geoids which is a clue indicating a rotation on itself as the Earth. Our code can set precise angular momentum in order to study the pattern of distortion from fission to multiple splitting. To evaluate the numbers of sub-cluster a Complete Clustering algorithm based on graph theory has been programmed exhibiting a linear complexity. To conclude a study of xenon doping is presented where the recombination dynamics unveils a metastable state called Atkins’ snowball [6] and different patterns of aggregation as nano- crystals and nano-wires well known by experimentalists
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Dates et versions

hal-04561076 , version 1 (26-04-2024)

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  • HAL Id : hal-04561076 , version 1

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Roland Panzou, Marius Lewerenz. Modelling of ultra-cold helium nanodroplet dynamics. Clustertreffen 2022, Oct 2022, Feldberg, Germany. ⟨hal-04561076⟩
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