Negative-ion/positive-ion coincidence analysis of ethanol
1University of Oulu, Faculty of Science, Physics
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Oulu : J. Koponen,
Negative-ion/positive-ion coincidence (NIPICO) spectroscopy is a type of ion time-of-flight mass spectroscopy, which was used to study ethanol. The measured data was then analyzed using Igor Pro 8 data analysis program. The goal of this thesis is to familiarize the reader in NIPICO and to understand its value in studying fragmentation channels of molecules and the physics behind it. Topics in this thesis are integral to NIPICO, from the production of synchrotron radiation, its usage in beamlines, to the instruments of measurements and all the way to data processing and analysis. Ethanol was chosen for this thesis for its wide-ranging fields of use and for its simplicity.
Photoinduced electronic transitions give information on the structure and dynamics of molecules. By studying the excitation, decay and fragmentation of molecules, more information about the interaction between photons and molecule can be acquired. Coincidence spectroscopy is a method of detecting and analyzing multiple particles simultaneously. It is used to study decay and dissociation processes by measuring molecule’s particle emissions and fragments.
The data in this thesis were measured using the gas-phase end station (GPES) of the FinEstBeAMS beamline of MAX IV synchrotron facility. Two time-of-flight spectrometers were used, one for negative ions and one for positive ions. The spectrometers were mounted opposite of each other, with a common interaction region, where the x-ray ionization and dissociation of the ethanol molecules happened.
The ethanol data was analyzed at three photon energies. The energies were chosen around the first O 1s resonance and the O 1s ionization threshold to see how the ethanol’s dissociation changed with the photon energy. The first O 1s resonance at 533.9 eV acted as the baseline, where the two other energies were compared to. The two other energies were 530 eV, which is below the first O 1s resonance and 541 eV, which is above the O 1s ionization threshold. O- and H- were the dominant anions in all the energies, with C-, C2- and OH- anions also detected. Negative-ion/positive-ion/positive-ion coincidence (NIPIPICO) series were detected with all the energies. Multiple negative-ion/positive-ion/positive-ion/positive-ion coincidence (NIPIPIPICO) series were also detected at 533.9 eV and 541 eV.
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