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Thermal properties of clusters and molecules - Experiments on evaporation, thermionic emission, and radiative cooling

Abstract
This thesis presents experiments performed on clusters and molecules, where the three channels of unimolecular decay have been studied. Evaporation from protonated and negatively charged water cluster have yielded size dependent heat capacities, where the smallest sizes with fewer than $21$ molecules show a heat capacity similar to bulk ice whereas clusters with molecules between $21$ and $300$ have a heat capacity in between that of ice and liquid water. The increase in heat capacity per added molecule in the cluster indicates that the intramolecular degrees of freedom are frozen at the temperatures in the experiment (T$\approx\!\!\!160$~K). Experiments on small mixed water-ammonia clusters resulted in relative evaporation fractions for sizes between a total of three to eleven molecules, and $16$ molecules. The clusters were found to evaporate predominantly water molecules except for clusters containing six or more ammonia molecules. Relative evaporation rates for D$_2$O, HDO, and H$_2$O were measured for NH$_4^+$(H$_2$O)$_4$ with zero to six deuteriums interchanged with the hydrogens. The relative rates were found to be $1:0.71:0.56$. Absolute timedependent cooling rates for hot C$_{60}^-$ were obtained in an electrostatic storage ring with single photon absorption experiment. The cooling of the molecule could be divided into a thermionic emission part and a radiative part, where the crossover between the two occurred at $5$~ms, after which radiation was shown to be the dominant cooling channel. The spontaneous decay profiles were used to extract decay parameters of the large organic anion zink phthalocyanine (ZnPc). Numerical simulations of the decay process show good agreement with measurements, using parameters derived from an analytical approximation also used for fullerenes. Photoabsorption experiments were performed on the much smaller C$_5^-$, showing the presence of strong radiative cooling. The cooling rate was determined by the dependence of the photoinduced neutralization yield vs. photon energy and laser firing time.
Parts of work
A. E. K. Sundén, K. Stöchkel, S. Panja, U. Kadhane, P. Hvelplund, S. Bröndsted Nielsen, H. Zettergren, B. Dynefors, and K. Hansen, (2009) Heat capacities of freely evaporating charged water clusters, Journal of Chemical Physics 130, 224308.::doi::10.1063/1.3149784
 
A. E. K. Sundén, K. Stöchkel, P. Hvelplund, S. Bröndsted Nielsen, B. Dynefors, and K. Hansen, (2012) Relative light and heavy water evaporation from NH_3(H_2O)_3H^+ clusters, Unpublished manuscript.
 
A. E. K. Sundén, M. Goto, J. Matsumoto, H. Shiromaru, H. Tanuma, T. Azuma, J. U. Andersen, S. E. Canton, and K. Hansen, (2009) Absolute cooling rates of freely decaying fullerenes, Physical Review Letters 103, 143001.::doi::10.1103/PhysRevLett.103.143001
 
M. Goto, A. E. K. Sund\'en, Y. Zama, H. Shiromaru, H. Tanuma, T. Azuma, J. Matsumoto, Y. Achiba, and K. Hansen, (2012) Radiative cooling of C_5^-, Unpublished manuscript.
 
Degree
Doctor of Philosophy
University
Göteborgs universitet. Naturvetenskapliga fakulteten
Institution
Department of Physics ; Institutionen för fysik
Disputation
Fredagen den 24 februari 2012, kl. 10.15, FB salen, Fysikgården 4, Chalmers, Göteborg
Date of defence
2012-02-24
E-mail
erika.sunden@physics.gu.se
URI
http://hdl.handle.net/2077/28349
Collections
  • Doctoral Theses / Doktorsavhandlingar Institutionen för fysik
  • Doctoral Theses from University of Gothenburg / Doktorsavhandlingar från Göteborgs universitet
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Thesis frame (1.613Mb)
Spikblad (143.1Kb)
Date
2012-02-03
Author
Sundén, Erika
Keywords
water clusters
fullerenes
unimolecular decay
evaporation
thermionic emission
radiative decay
cooling rates
heat capacities
Publication type
Doctoral thesis
ISBN
978-91-628-8429-1
Language
eng
Metadata
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