Resonance Electron Capture Mass Spectrometry (REC-MS) is a sensitive
experimental technique for the study of gas-phase compounds with positive electron
affinity. This technique was used to study a class of compounds known as
baloetbylenes containing chlorine and bromine substitutions. Haloetbylenes are an
important class of compounds because ethylene is the simplest model system for
studying resonance electron capture for larger π bond networks and the effects of
substitution, both in position and type. Secondly, haloethylenes are environmental
contaminants that result from large-scale industrial use thereby making it important to
study methods that can produce additional specificity in environmental analysis and
assist in unambiguously identifing the specific compound(s) present.
Through experimentation a correlation was found showing that increasing
chlorine substitution resulted in a lowering of the effective yield maximum for Cl⁻ in
chioroethylenes and that these chioroethylenes can be identified by the shape and
maxima of the yield curves. Additional fragmentation channels not previously observed were recorded and molecular ions (Mt) were observed for
tetrachioroethylene and trichioroethylene, which were not previously known to exist.
Higher energy fragmentations (6-10 eV) most likely result from Feshbach resonances
involving the neutral (N) electronic to singlet (S) state transition. The effective yield
maximum at 8 eV for production of the C₂Cl⁻ from tetrachioroethylene represents a
special case and may result from a Feshbaeh resonance at the ionization potential of
the parent molecule.
Bromoethylenes have effective yield maxima that result from lower energy
electron attachment for comparable fragmentation channels for chioroethylene
species. A total of seven channels not having a maximum near zero eV were observed
in bromoethylenes. No molecular ions were observed in any of the bromoethylenes
studied. Theoretical studies show that the vertical electron attachment energy of a
compound is dependent upon the type, number, and location of substituents while the
adiabatic electron affinity is dependent upon the type and number of substituents but
not on the regiochemistry. Additional theoretical work has led to a new explanation
for Cl⁻ fragment ions that occur with electrons of near to zero eV energy from
tetrachioroethylene as possibly arising through a predissociation mechanism that
allows for π* and σ* mixing in a non-coplanar structure of the negative ion.
Additional work was done to improve data analysis by developing a Visual
Basic (VB) based software to parse data in output flIes. The program was entitled
"Extractor" and resulted in a dramatic savings in time for data processing.
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