Formation of Positively Charged Liquid Helium Clusters in Supercritical Helium and their Solidification upon Compression

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• 作者：Hejer Gharbi Tarchouna ; Nelly Bonifaci ; Fr茅d茅ric Aitken ; Luis Guillermo Mendoza Luna ; Klaus von Haeften
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2015
• 出版时间：August 6, 2015
• 年：2015
• 卷：6
• 期：15
• 页码：3036-3040
• 全文大小：282K
• ISSN：1948-7185

文摘

Positively charged ions were produced in supercritical helium at temperatures from 6 to 10 K and up to 2 MPa using a corona discharge. Their mobility was measured via current鈥搗oltage curves, and the hydrodynamic radius was derived using Stokes law. An initial increase and subsequent decrease of hydrodynamic radius was observed and interpreted in terms of growth, compression and solidification of ion clusters. The mobility was modeled using a van der Waals-type thermodynamic state equation for the ion-in-helium mixed system and a temperature-dependent Millikan-Cunningham factor, describing experimental data both in the Knudsen and the Stokes flow region. Regions of maximum hydrodynamic radius and large compressibility were interpreted as boiling points. These points were modeled over a large range of pressures and found to match the Frenkel line of pure helium up to 0.7 MPa, reflecting similarity of density fluctuations in pure supercritical helium and gas鈥搇iquid phase transitions of ionic helium clusters.