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Vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters

Authors: Ahmed, Musahid Wilson, Kevin R. Belau, Leonid Kostko, Oleg
 
Abstract: In this work we report on thevacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuumultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH + (n=1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH)n(H2O)H + (n=2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH +, (CH 3OH)2 +, (CH3OH)nH + (n=1-9), and (CH 3OH)n(H2O)H + (n=2-9 ) as a function of photon energy. With an increase in the water content in the molecular beam, there is an enhancement of photoionization intensity for methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.
Publication Date: 12 May 2008
Report numbers: LBNL-262E
DOE Contract number: DE-AC02-05CH11231
Resource Type: Journal Article
Resource Relation: Journal: The Journal of Physical Chemistry
Research Organizations: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
Sponsoring Organizations: Chemical Sciences Division
Country of Publication: United States
Language: English
Keywords relating to this report:
DIMERS
EFFICIENCY
IONIZATION
MASS SPECTROSCOPY
METHANOL
MOLECULAR BEAMS
MONOMERS
PHOTOIONIZATION
PHOTONS
SYNCHROTRON RADIATION
WATER