dorsal/arxiv
View SchemaPotential of a neutral impurity in a large $^4$He clusters
| Authors | Kevin K. Lehmann |
|---|---|
| Categories | |
| ArXiv ID | physics/9905010 |
| URL | https://arxiv.org/abs/physics/9905010 |
| DOI | 10.1080/002689799163497 |
| Journal | Mol. Phys. 82, 645-666 (1999) |
Abstract
This paper presents an analysis of the motion of an neutral impurity species in a nanometer scale $^4$He cluster, extending a previous study of the dynamics of an ionic impurity. It is shown that for realistic neutral impurity-He potentials, such as those of SF$_6$ and OCS, the impurity is kept well away of the the surface of the cluster by long range induction and dispersion interactions with He, but that a large number of `particle in a box' center of mass states are thermally populated. It is explicitly demonstrated how to calculate the spectrum that arises from the coupling of the impurity rotation and the center of mass motion, and it is found that this is a potentially significant source of inhomogeneous broadening in vibration-rotation spectra of anisotropic impurities. Another source of inhomogeneous broadening is the hydrodynamic coupling of the rotation of the impurity with the center of mass velocity. A quantum hamiltonian to describe this effect is derived from the classical hydrodynamic kinetic energy of an ellipsoid. Simple analytic expressions are derived for the resulting spectral line shape for an impurity in bulk He, and the relevant matrix elements derived to allow fully quantum calculations of the coupling of the center of mass motion and rotation for an impurity confined in a spherical He cluster. Lastly, the hydrodynamic contribution to the impurity effective moment of inertia is evaluated and found to produce only a minor fractional increase.
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"abstract": "This paper presents an analysis of the motion of an neutral impurity species\nin a nanometer scale $^4$He cluster, extending a previous study of the dynamics\nof an ionic impurity. It is shown that for realistic neutral impurity-He\npotentials, such as those of SF$_6$ and OCS, the impurity is kept well away of\nthe the surface of the cluster by long range induction and dispersion\ninteractions with He, but that a large number of `particle in a box\u0027 center of\nmass states are thermally populated. It is explicitly demonstrated how to\ncalculate the spectrum that arises from the coupling of the impurity rotation\nand the center of mass motion, and it is found that this is a potentially\nsignificant source of inhomogeneous broadening in vibration-rotation spectra of\nanisotropic impurities. Another source of inhomogeneous broadening is the\nhydrodynamic coupling of the rotation of the impurity with the center of mass\nvelocity. A quantum hamiltonian to describe this effect is derived from the\nclassical hydrodynamic kinetic energy of an ellipsoid. Simple analytic\nexpressions are derived for the resulting spectral line shape for an impurity\nin bulk He, and the relevant matrix elements derived to allow fully quantum\ncalculations of the coupling of the center of mass motion and rotation for an\nimpurity confined in a spherical He cluster. Lastly, the hydrodynamic\ncontribution to the impurity effective moment of inertia is evaluated and found\nto produce only a minor fractional increase.",
"arxiv_id": "physics/9905010",
"authors": [
"Kevin K. Lehmann"
],
"categories": [
"physics.chem-ph"
],
"doi": "10.1080/002689799163497",
"journal_ref": "Mol. Phys. 82, 645-666 (1999)",
"title": "Potential of a neutral impurity in a large $^4$He clusters",
"url": "https://arxiv.org/abs/physics/9905010"
},
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