Our prime interest of the AFOSR program is to support combustion related research which pro­vides data and procedures to enable the development of reliable chemical propulsion systems. The latter should be able to quantitatively predict the performance of combustion and propellant systems to mini­mize the emis­sion of unwanted by-products and to maximize the propulsion efficiency. However, all models simulating chemical propulsion systems require crucial input parameters such as the knowledge of 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, and the assign­ment of the primary reaction products together with branching ratios. Based on these data, the ultimate goal is to predict and to eliminate instabilities and to optimize the efficiency of chemically-based propulsion systems.

The main goals of our current research are to elucidate the energetics and the dynamics of reactions of ground state boron atoms, B(²P_j), with unsaturated hydrocarbons acetylene (C₂H₂), ethylene (C₂H₄), me­thyl­­ace­tylene (CH₃CCH), allene (H₂CCCH₂), and benzene (C₆H₆). 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 pooled together with elec­­­tro­­nic struc­tu­re cal­­cu­­lations to verify the elucidated re­ac­ti­on me­cha­­ni­sms the­­­o­re­tically.

Currently we are carrying out the ex­peri­­ments under single collision conditions em­ploy­ing a hydro­car­bon-free crossed molecular beams machine at various collision energies from 8–40 kJmol^-1; to identify the position of the atomic hydrogen loss, we also conducted selected experiments with partially deuterated hydrocarbons such as D3-methylacetylene. In the present configuration of the machine, angular resolved time-of-flight spectra are recorded to detect the reaction products with the help of a triply differentially pumped, rotatable quadrupole mass spectrometer and electron impact ionizer at 200 eV electron energy. The underlying dynamics suggest that all reactions have no entrance barrier, are exoergic, proceed via indirect scattering dynamics via an initial addition of the boron atom to the unsaturated carbon-carbon bond followed by hydrogen atom shift, and are terminated by an atomic hydro­gen loss pathway; upper limits of the molecular hydrogen loss channel were derived to be 1 %.  We are currently testing  a new ionizer so that an operation under ‘soft electron impact ionization’ is feasible. This allows to ionize and discriminate reaction products based on their distinct ionization potentials. Current tests depict stable operation conditions of up to 1.0 mA at an electron energy of 8 eV. Details of the reaction dynamics can be found in our publications and presentations; the corresponding files are updated periodically once a paper is in its final proof stage. This research is supported by the Air Force Office of Scientific Research (AFOSR). To obtain information on this funding agency, please click on the AFOSR icon above.

Test runs of the new ionizer utilizing 'soft and tunable electron impact ionization'.

The Crossed Beams Machine Publications Research Presentation Links