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Heat capacities of freely evaporating charged water clusters

Erika Sundén ; K Stöchkel ; S Panja ; U Kadhane ; P. Hvelplund ; S. Brøndsted Nielsen ; H. Zettergren ; Bertil Dynefors (Institutionen för teknisk fysik) ; Klavs Hansen
Journal of Chemical Physics (0021-9606). Vol. 130 (2009), 22, p. 224308.
[Artikel, refereegranskad vetenskaplig]

We report on evaporation studies on positively charged water clusters (H$^+$(H$_2$O)$_N$) and negatively charged mixed clusters (X$^-$(H$_2$O)$_N$) with a small core ion $X$ ($X$=O$_2$,CO$_3$ or NO$_3$), in the size range $N=5$ to $300$. The clusters were produced by corona discharge in ambient air, accelerated to 50 keV and mass selected by an electromagnet. The loss of monomers during the subsequent 3.4 m free flight was recorded. The average losses are proportional to the clusters' heat capacities and this allowed the determination of size-dependent heat capacities. The values are found to increase almost linearly with clusters size for both species, with a rate of 6-8 $k_B$ per added molecule. For clusters with $N<21$ the heat capacities per molecule are lower but the incremental increase higher. For $N>21$ the values are intermediate between the bulk liquid and the solid water 0 $^o$C values.

Nyckelord: water clusters, thermodynamics properties

Denna post skapades 2009-10-22. Senast ändrad 2013-10-29.
CPL Pubid: 100537


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