Study of Low Energy Electron-Impact Induced Ionization and Fragmentation of Uracil

The aim of this experiment is to study low energy electron impact induced ionization and fragmentation of uracil. The apparatus consists of a pumped vacuum system with an expansion chamber, a collision chamber and a flight tube. A beam of uracil is generated in the expansion chamber, passes through a skimmer and crossed with a pulsed beam of low energy electrons in the collision chamber. The electron gun has a pulse width of 1 μs providing the necessary time of flight resolution and incorporates a deflection system for the steering of the beam. Positive ion fragments are mass resolved and detected using a reflectron time of flight mass spectrometer with a microchannel plate detecter. A multichannel scaler card is used for data acquisition. Code written in LabVIEW is used to control the electron impact energy and the acquisition of mass spectra as a function of electron impact energy. Ion yield curves for positive fragments are obtained from the mass spectra. Ion yield curves and appearance energies have been obtained from our data set and are in good agreement with results from previous research and other research groups. Partial ionization cross sections have been obtained by normalization of the sum of the ion yield curves to the average of calculated total ionization cross sections at 70 eV. These results provide new information about the fragmentation pathways initiated by electron impact and the cross sections for production of these ions. This research is relevant in the study of low energy secondary electron interactions within biological organisms. The aim of this research is to better understand the fundamental reaction mechanisms leading to DNA strand breaks. The experiment also includes the development and testing of a supersonic source using a 50 micron straight nozzle with argon gas acting as the buffer gas. The supersonic source will improve beam collimation and will enable formation of small nucleobase-water clusters when water vapour is introduced into the source.

Level dc:type.qualificationlevel

masters

Grantor dc:publisher.institution

National University of Ireland Maynooth

Year dc:date.issued

2016

Author dc:creator

• Diskin, Steven

Language dc:language

en