The major
interest of our
research is to explore potential energy surfaces (PES) relevant to the
formation of hydrogen deficient, often resonantly stabilized
hydrocarbon
radicals of the generic formulae C3Hx, C4Hx,
C5Hx, and C6Hx (x = 1 – 6)
experimentally
utilizing the crossed molecular beams technique. These molecules are of
crucial
importance to understand the formation of the first aromatic ring
molecules and
their corresponding radicals in combustion flames. The information help
to
quantitatively predict via models the performance of combustion systems
and
minimize the emission of unwanted by-products such as
polycyclic aromatic
hydrocarbons (PAHs) as well as soot particles; likewise, energy
conservation
will be maximized and environmental protection is going to be
improved.
However, all combustion models require crucial input
parameters such as rate
constants of the chemical reactions over a wide
temperature and pressure
range, the identification of reaction intermediates, which either form
products, are stabilized via three body reactions, react with
other molecules,
or decay back to the reactants. Likewise, an assignment of
the primary
reaction products together with the branching ratios is crucia.
The goal
of our present
project is to untangle the energetics and the dynamics of reactions of
ground
and excites state dicarbon, C2, and of ground state
tricarbon
molecules, C3, with unsaturated hydrocarbons acetylene (C2H2),
ethylene (C2H4), methylacetylene (CH3CCH),
allene (H2CCCH2), and benzene (C6H6)
at collision energies of 10-50 kJmol-1 and 72-175
kJmol-1,
respectively. These reactions are of fundamental importance to
understand the
formation of carbonaceous nanostructures as well as polycyclic aromatic
hydrocarbons and their hydrogen deficient precursors in combustion
flames. The
closed shell hydrocarbons serve as prototype reaction partners with
triple
(acetylene), double (ethylene), and aromatic (benzene) bonds;
methylacetylene
and allene are chosen as the simplest representatives of closed shell
hydrocarbon species to investigate how the reaction dynamics change
from one
structural isomer to the other. The experiments are carried out under
single
collision conditions employing a novel crossed molecular beams machine
at The University of Hawai’i. These investigations
identify the chemical dynamics, reaction mechanisms, reaction
products, the energetics
and entrance barriers of the reaction, the intermediates involved,
the
branching ratios, and experimental enthalpies of formation of
hydrocarbon molecules
and their radicals - data which are very much required by the
combustion
chemistry community. The newly commissioned ‘soft ionization method’
will
enable us also to supply ionization potentials of various
hydrocarbon
molecules. The experiments are pooled together with electronic
structure
calculations in collaboration with Prof. Alexander M. Mebel (Florida
International
University)
to verify the elucidated reaction mechanisms
theoretically. Finally, all data will be incorporated into combustion
models in
collaboration with Prof. Michael Frenklach (UC Berkeley).
The
studies suggest the formation
of various C4Hx (x = 1-4), C5Hx (x = 1-4), and C6 H x (x = 3, 4) intermediates and final reaction products formed via atomic
and
molecular hydrogen elimination channels. These molecules can access,
for
instance via reactions with CH3, C4H5,
and C5H5 radicals, to access the C6H6 and C10H8 potential energy surfaces potentially leading to the formation of
benzene,
naphthalene, and azulene together with their structural isomers.
Details of the
reaction dynamics can be found in our publications; the corresponding
pdf files
are updated periodically once a paper is in its final proof stage. This
research is supported by the US Department of Energy (DOE-BES). To
obtain
information on this funding agency, please click on the DOE-BES icon
above.Very recently, these studies have been
expanded to access various regious of the singlet and triplet C6H6 as well as doublet C6H5 PESs. These investigations help us
to
study the underlying isomerization processes to form benzene and the
phenyl radical - two crucial intermediates in combustion flames.
Important
intermediates identified in the
reactions of dicarbon molecules with unsaturated hydrocarbons.
Important
reaction products identified in the
reactions of dicarbon molecules with unsaturated hydrocarbons.
Important
intermediates identified in the
reactions of tricarbon molecules with unsaturated hydrocarbons.
Important
reaction products identified in the
reactions of tricarbon molecules with unsaturated hydrocarbons.
The Crossed Beams Machine
Publications
Research Presentation
Links
