3. The Fleet

 

 

 

 

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W.M. Keck Laboratory in Astrochemistry

High Temperature Chemical Reactor

Surface Scattering Machine

Crossed Beam Machine

Levitation Device

Liquid Nitrogen Facility

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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 (boron, carbon, nitrogen, oxygen, silicon), polyatomic radicals (cyano [CN], boron monoxide [BO], methylidyne [CH], ethynyl [C2H], vinyl [C2H3], propargyl [C3H3], allyl [C3H5], phenyl [C6H5], hydroxyl [OH], and most recently silicon monohydride [SiH], silicon nitride [SiN], silicon carbide [SiC], and silicon monoxide [SiO]) 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. Complementary to the crossed beam approach, combustion-relevant experiments on the formation of polycyclic aromatic hydrocarbons (PAHs) and their non-PAH isomers are also conducted in collaboration with Dr. Musahid Ahmed (Lawrence Berkeley Laboratory) in a high-temperature chemical reactor simulating combustion relevant conditions. 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).

 

 

 

 

 

 

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Two surface scattering machines investigate the interaction of ionizing radiation (electrons, atomic and molecular ions, tunable photons) with low temperature ice surfaces down to 4 K. These ices can be 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 chemical reactions and kinetics 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 to 500 cm-1), UVVIS spectroscopy (190-800 nm; 6.5-1.1 eV), Raman (15,000 to 100 cm-1), UVVUV spectroscopy (5.0 to 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 to 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.

 

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We are currently merging an ultrasonic levitation device with a pressure-compatible process chamber to study heterogeneous reactions on freely levitated soot analog particles leading to the formation of polycyclic aromatic hydrocarbon molecules and soot at temperatures from 300 K to a few 1,000 K and pressured from 10 Torr to 2280 Torr. By heating the levitated particles to combustion-relevant temperatures with the help of a carbon dioxide laser, surface reactions with aromatic (phenyl) and resonantly stabilized free radicals (propargyl, allyl) from the gas phase are triggered. Utilizing cryo-cooling, this setup is also capable to investigate the photochemical processing of (ice coated) micrometer sized organic and mineral-based grain particles as analog particles of interplanetary grains, cometary dust, and planetary ring particles at temperatures as low as about 80 K. This machine will be interfaced to complimentary, non-evasive spectroscopic probes (Infrared, Raman, UVVIS) thus enabling us to chemically characterize the levitated particles and their chemical modifications.

 

   

                            

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