Study of Electron-Impact Induced Fragmentation of Thymine

The aim of the experiment described in this thesis was to generate a molecular beam of thymine and to investigate the fragmentation processes induced by low-energy electron impact. A molecular beam of thymine is generated by placing thymine in powder form inside a resistively heated oven. The beam of thymine is then crossed by a pulsed electron beam from an electron gun that consists of four electrostatic lens elements and a deflection system for steering the beam. A reflectron time-of-flight mass spectrometer with a microchannel plate detector is used to detect and mass resolve the positively charged fragments. LabVIEW based data acquisition techniques are used to accumulate the time-of-flight data as a function of electron impact energy. The work described in this thesis is based on a single data set of thymine with electric impact energy varied from 0.5 to 99.7 eV in steps of 0.5 V. To determine the yield of the various fragment ions, groups of peaks were fitted with a sequence of normalised Gaussian peaks using a specially developed LabVIEW program. Using this program the fitting of the peaks was done automatically for all electron energies. Excitation functions for the most positively ionised fragments have been extracted/or determine and their appearance energies have been determined and compared to current research on thymine. Because all excitation functions have been generated from this single data set and assuming that the detection efficiency of the RTOFMS is mass independent, the yield of all fragments are on the same relative scale and are comparable. Total ionisation cross sections have been obtained for our data set and are in good agreement with theoretical calculations.

Level dc:type.qualificationlevel

masters

Grantor dc:publisher.institution

National University of Ireland Maynooth

Year dc:date.issued

2013

Author dc:creator

• Mahon, Francis Anthony

• Experimental Physics

Language dc:language

en