Classical and quantum molecular dynamics simulations of dissociation after electron impact in plasma

This thesis concerns itself with the application of existing non-adiabatic
molecular dynamics methods, namely Ab Initio Multiple Cloning, to
a novel application of neutral dissociation of molecules after electronic
excitation via electron impact. This process is particularly important
in the context of plasma etching of semiconductors, as understanding
the dissociation pathways can aid in the design of new precursors that
are more environmentally friendly and selective in their etching pro-
cess. Electronic excitation cross-sections indicate that excitation via
electron impact primarily causes population of triplet states. These
simulations were performed with Ab Initio Multiple Cloning, though
it is also shown that a significant portion of the molecules require only
the inclusion of the lowest triplet state, and therefore more computa-
tionally efficient standard molecular dynamics are sufficient.
The simulations reveal that analogous to the chromophores that
localise photo excitation, there exist certain functional groups, termed
electrophores, that localise the excitation via electron impact and
therefore also localise the dissociative character of the triplet state.
Neutral dissociation pathways are analysed for currently researched
plasma precursors. The oxygen atom is identified as playing a key role
in the determining of dissociation pathways, with the findings of the
molecular dynamic simulations identifying the same weak bonds found
in Quadrople Mass Spectrum experiments. The interaction between
the oxygen and the C=C bond that was found to be an electrophore
previously suggest that a hierarchy of electrophores can be developed.
These electrophores can be used to at least qualitatively predict the
neutral dissociation pathways of the molecules without the need for
simulations.
Finally, the cloning procedure that is the namesake for Ab Initio
Multiple Cloning is introduced to the first version of the Multicon-
figurational Ehrenfest method. This new extension of can be called
Full Cloning MCEv1 as it requires the cloning of the entire basis set.

Full Cloning MCEv1 is benchmarked against the Multiconfigurational
Time Dependent Hartree method in the zero temperature regime of
the spin boson model, where it showed improved convergence and
accuracy.
These results together represent both a theoretical development in
the non-adiabatic dynamics community as well as laying the found-
ation for the application of these methods to a new area of neutral
dissociation in plasma etching, supporting the development of cleaner,
more selective plasma chemistries.