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Sodium-cluster complexes : probability of formation, stability and mass spectra

University of British Columbia

Accurate knowledge of aerosol size and composition is important for the understanding of their effects on both the atmosphere and the health of those who inhale them. Ultrafine aerosols (0.25 nm to 10 nm radius) and small clusters (2 molecules to 0.25 nm radius) can only be detected down to radii of a few nanometers and no chemical information is provided. A photoion spectrometer was previously built and is used to dope clusters and ultrafine aerosols with Na atoms. The subsequent Na-cluster complexes are then ionized by a UV laser. This technique is currently believed to be the softest ionization method available. Calculations were done to predict the efficiency of this system because a direct comparison with other systems cannot be made over the complete size range. These calculations include, the probability of a particle colliding with a Na atom in the oven, the average lifetime of Na-cluster complexes and their photoionization efficiency. Calculations in this thesis focus on the collision probability and include predictions as to the most efficient temperature of the Na oven for Na pick up. The temperature of the Na oven was also found to experimentally agree with the calculations, because the vapor pressure of Na plays a significant role in the collision probability. Characterization of the sodium doping technique was done through experiments comparing direct XUV ionization with UV ionization of small Na doped clusters. The fragmentation of acetic acid clusters was characterized for the monomer and oligomers up to the tetramer. It was found that up to two acetic acid molecules evaporated from the clusters. The Na doping technique also reveals a significant difference in the size distribution as seen by UV and XUV laser ionization for large dimethyl ether and acetic acid clusters, and a smaller yet visible difference for large water clusters. Different UV wavelengths were also investigated including wavelengths above and below the ionization energy of a lone Na atom. The Na doping technique was found to be a softer technique than direct ionization with XUV light, because no fragmentation of molecules occurred and evaporation was minimized.

Text

2012-04-11

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/41966

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/