Velocity distribution function of Na released by photons from planetary surfaces

Gamborino Uzcanga, Diana; Wurz, Peter (2018). Velocity distribution function of Na released by photons from planetary surfaces. Planetary and space science, 159, pp. 97-104. Elsevier 10.1016/j.pss.2018.04.021

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In most surface-bound exospheres Na has been observed at altitudes above what is possible by thermal release. Photon stimulated desorption of adsorbed Na on solid surfaces has been commonly used to explain observations at high altitudes. We investigate three model velocity distribution functions (VDF) that have been previously used in several studies to describe the desorption of atoms from a solid surface either by electron or by photon bombardment, namely: the Maxwell-Boltzmann (M-B) distribution, the empirical distribution proposed by [1] for PSD, and the Weibull distribution. We use all available measurements reported by [2, 3] to test these distributions and determine which one fits best (statistically) and we discuss their physical validity. Our results show that the measured VDF of released Na atoms are too narrow compared to Maxwell-Boltzmann fits with supra-temperatures as suggested by [3]. We found that a good fit with M-B is only achieved with a speed offset of the whole dis- tribution to higher speeds and a lower temperature, with the offset and the fit temperature not showing any correlation with the surface temperature. From the three distributions we studied, we find that the Weibull distribution provides the best fits using the temperature of the surface, though an offset towards higher speeds is required. This work confirms that Electron-Stimulated Desorption (ESD) and Photon-Stimulated Desorption (PSD) should produce non-thermal velocity (or energy) distributions of the atoms released via these processes, which is expected from surface physics. We recommend to use the Weibull distribution with the shape parameter κ ¼ 1.7, the speed offset v 0 ¼ 575 m/s, and the surface temperature to model PSD distributions at planetary bodies

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Gamborino Uzcanga, Diana and Wurz, Peter

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

0032-0633

Publisher:

Elsevier

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

18 Jul 2018 08:13

Last Modified:

23 Jul 2018 11:35

Publisher DOI:

10.1016/j.pss.2018.04.021

BORIS DOI:

10.7892/boris.118606

URI:

https://boris.unibe.ch/id/eprint/118606

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