|
|
3. The Fleet
|
|
|
|
|
|
|
|
|
|
|
The
prime directive of our research is to experimentally study the dynamics of
chemical reactions in extreme environments like combustion systems, rocket
engines, chemical vapor deposition processes, and extraterrestrial
environments (interstellar medium, solar system, comets, astrobiological
habitats). In our crossed molecular beams machine, we use photolytic,
pyrolytic, and laser ablation techniques to generate supersonic beams of
neutral atoms (carbon, boron, silicon, nitrogen, oxygen), polyatomic radicals
(cyano, ethynyl, phenyl, propargyl, vinyl, allyl, hydroxyl) and clusters
(dicarbon, tricarbon). The chemical reactions are initiated under single
collision conditions by crossing such beams with a second supersonic beam
containing radicals or closed shell species. By recording angular resolved
time of flight (TOF) spectra, we can obtain information on the nascent
reaction products, intermediates involved, on branching ratios for competing
reaction channels, on the energetics of the reaction(s), and the underlying
reaction mechanisms. An on-axis beam characterization is conducted
spectroscopically via laser induced fluorescence (LIF) and via TOF mass
spectrometry utilizing (tunable) electron impact ionization of the neutral
molecules. This research helps to understand elementary reaction mechanisms
with applications to combustion chemistry, rocket propulsion systems,
extraterrestrial chemistry, and chemistry in our Solar System such as in
Titan's atmosphere. These projects are supported by (in alphabetic order) the
Air Force Office of Scientific Research (AFOSR), the Department of Energy
(DOE-BES), and by the National Science Foundation (NSF-CHE; NSF-CRC). |
||
|
|
|
|
|
|
|
|
|
|
|
|
|
Two
surface scattering machines investigate the interaction of energetic
particles (electrons, atomic and molecular ions, photons of tunable energies,
neutral atoms) with low temperature ice surfaces down to 4 K. These
‘ices’ are either neat like water, methane, ammonia, carbon
monoxide, carbon dioxide, nitrogen, oxygen or complex mixtures with minerals.
By inducing non-equilibrium chemistry, we can follow the reaction in real
time on line and in situ. The information obtained are data on reaction
products, their formation rates, and information on the kinetics and
dynamics. The reaction intermediates and products are analyzed on line and in
situ via infrared spectroscopy (15,000 – 500 cm-1), UVVIS
spectroscopy (190-800 nm; 6.5-1.1 eV), Raman (15,000 ~ 10 cm-1),
UVVUV spectroscopy (5.0 – 11.8 eV), mass spectrometry (residual gas
analyzer mode; tunable electron impact ionization from a few eV to 80 eV with
emission currents of up to 4 mA), and UVVUV photoionization of the neutral
molecules and analyzing the ionized species in a reflectron TOF-MS (5.0
– 16.0 eV). Tunable UVVUV is generated via sum and difference resonance
four wave mixing schemes utilizing either gas cells (Kr, Xe, Hg) or pulsed
jet expansions (Kr, Xe).These findings can be utilized to better understand
the chemistry of interstellar grains and in our Solar System (icy planets and
their moons; Kuiper Belt Objects). Our research is supported by (in
alphabetic order) the National Aeronautics and Space Administration (NASA)
and by the W.M. Keck Foundation.
|
||
|
|
|
|
|
|
|
|
