| dc.description.abstract | This thesis is an amalgam of two largely different experiments. While the exper-
imental apparatus are similar, the incident particles, fundamental interactions, and
dissociation dynamics of the two systems are entirely different. They are tied together
via momentum spectroscopy, occasionally called the ”momentum microscope”. The
two experiments each represent a fundamental pillar of the modern scientific regime.
For one, it is an observational first, producing an experiment that no other research
group has produced before. For the other, it is a check on reproducibility, an effort
by the scientific community to validate its efforts.
0.1 Water Experiment
The first of the two experiments included in this thesis is the double photoion-
ization of water by 57 eV linearly polarized photons. A 57 eV photon collides with
a water molecule and excites two molecular bonding electrons into the continuum.
The remaining dication, H2O2+, is generally considered unstable and has not been
observed in the laboratory. The unstable dication breaks apart, according to the
multi-dimensional potential energy surface(s) available to it. The momentum for
each of the charged particles - two protons and two electrons - are measured in co-
incidence. The measurement of the two protons allows for the full orientation of the
water molecule prior to dissociation. Prior to the writing of this thesis, this has only
been achieved in a ”recoil axis” frame, aligning two fragments of a complex molecule
that breaks apart upon one bond, including the simplest case of a diatomic molecule.
The full three dimensional momentum resolution of the entire molecule, and its pho-
toelectrons, is new terrain in momentum spectroscopy. The energies of the recoil
ions and electrons, as well as their angular distributions, are measured and analyzed
in an attempt to match the repulsive dication states of the water molecule to the
asymptotic fragment configurations in both two- and three-body reaction pathways.
The water experiment was conducted at the ALS with other members of the
COLTRIMS collaboration from Kansas State University, University of Frankfurt,
and Auburn University. The data was given to the author of this thesis as a training
exercise in data analysis - training on the actual acquisition of data using COLTRIMS
came later, in the second experiment of this thesis.
The details of the experimental apparatus, the excitation of the dication, and
its subsequent decay are the focus of the first two chapters of this thesis.
0.2 CF4 Experiment
The second experiment is dissociative electron attachment to C F4. Electron at-
tachment is an electron scattering interaction wherein a low energy electron, typically
from 0-15 eV in energy, collides with a molecule and is trapped in a local potential
minimum, a so-called Shape Resonance. Alternately, the electron can collide with
the molecule and couple with some internal degree of freedom, forming a negative
ion, a so-called Feshbach Resonance. These thesis chapters focus on the situation in
which the electron attachment leads to a dissociative negative ion state, with inci-
dent electron energies ranging from 5.5 eV to 9 eV. The angular distributions found
match, at least qualitatively, those of previous experiments, although the precise
partial wave analysis of those distributions disagree slightly with the literature. The
most interesting data, those taken as the primary motivation for the experiment,
are the KER measured as a function of the incident electron energy for the reaction
pathway leading to C F3−. These results disagree with the most recent results in the
literature which, on their own, disagreed with all the previous results in measurement
of this quantity.
The maintenance, repair, and troubleshooting of a COLTRIMS experiment are
rigorous endeavors, and the C F4 experiment gave the author of this dissertation
the opportunity to learn the minutiae of the complex experimental procedure. This
process took place, chronologically speaking, well after the analysis of the water
experiment was under way. While this ordering of training may initially appear
backwards, it was an invaluable layering of technical training, granting the author
many opportunities to revisit the skills required as a physicist, from deep literature
searches to vacuum pump maintenance to data analysis. | en_US |
