Dunne, Melissa Anne
(2017)
Low-Energy Electron Impact Fragmentations
of the Polycyclic Aromatic Hydrocarbon
Anthracene.
Masters thesis, National University of Ireland Maynooth.
Abstract
The aim of the study undertaken for this Masters of Science thesis was to investigate the
fragmentation processes induced by low-energy electron impact with anthracene. This
research is relevant in the study of low-energy electron interactions with molecules in
gaseous environments, including potentially in the interstellar medium where secondary
electrons may be produced by UV-irradiation of interstellar dust grains.
An effusive, molecular beam of anthracene, generated in a resistively heated oven, is
crossed with a beam of low-energy electrons to form positively charged fragments. A
reflectron time-of-flight mass spectrometer with a microchannel plate detector is used to
mass-resolve and detect the fragment ions.
A multichannel scaler card is used for acquiring single mass spectra. Data acquisition is
controlled by LabVIEW code, which ramps the electron impact energy from 0 to 100 eV
in 0.5 eV steps, acquires mass spectra as a function of electron impact energy, and adds
each mass spectrum to the data that has already been accumulated. The full data set
consists of a two-dimensional array of ion yield as a function of time-of-flight and of
electron impact energy. Ion yield curves of most of the fragment ions have been
determined by fitting groups of adjacent peaks in the mass spectra with sequences of
normalized Gaussians. This is done using in-house LabVIEW software. The appearance
energies for these fragments have been determined.
The groups of fragments containing 8 to 13 carbon atoms provide evidence for hydrogen
rearrangements during fragmentation, involving the retention or loss of one or two
additional hydrogen atoms. Groups of fragments with 6 and 7 carbon atoms clearly show
the presence of doubly-charged fragments. We see broadened peaks in the lower-mass
groups with 1 to 4 carbon atoms, which may be due to energetic charge-separation
fragmentations of doubly-charged anthracene.
| Item Type: |
Thesis
(Masters)
|
| Keywords: |
Low-Energy Electron; Impact; Fragmentations;
Polycyclic Aromatic Hydrocarbon Anthracene; |
| Academic Unit: |
Faculty of Science and Engineering > Experimental Physics |
| Item ID: |
9906 |
| Depositing User: |
IR eTheses
|
| Date Deposited: |
11 Sep 2018 14:42 |
| URI: |
|
| Use Licence: |
This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available
here |
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