No abstract

A conventional membrane-type stainless steel shock tube has been coupled to a high-repetition-rate time-of-flight mass spectrometer (HRR-TOF-MS) to be used to study complex reaction systems such as the formation of pollutants in combustion processes or formation of nanoparticles from metal containing organic compounds. Opposed to other TOF-MS shock tubes, our instrument is equipped with a modular sampling unit that allows to sample with or without a skimmer. The skimmer unit can be mounted or removed in less than 10 min. Thus, it is possible to adjust the sampling procedure, namely, the mass flux into the ionization chamber of the HRR-TOF-MS, to the experimental situation imposed by species-specific ionization cross sections and vapor pressures. The whole sampling section was optimized with respect to a minimal distance between the nozzle tip inside the shock tube and the ion source inside the TOF-MS. The design of the apparatus is presented and the influence of the skimmer on the measured spectra is demonstrated by comparing data from both operation modes for conditions typical for chemical kinetics experiments. The well-studied thermal decomposition of acetylene has been used as a test system to validate the new setup against kinetics mechanisms reported in literature.

At temperatures between 1150 and 2000 K and pressures between 0.1 and 0.2 MPa, the thermal decomposition of carbon suboxide (C(3)O(2)) behind reflected shock waves was investigated with a high-repetition-rate time-of-flight mass spectrometer (HRR-TOF-MS) connected to the end flange of a shock tube enabling rapid repetitive (100 kHz) measurements of the gas-phase composition. Concentration-time profiles for C(3)O(2) and CO were measured and compared to simulations based on an improved mechanism for C(3)O(2) decomposition and carbon cluster growth. In addition, relative concentrations of C atoms and C(2) molecules were detected and related to model predictions. For temperatures up to 1800 K, satisfactory agreement between experimental data and calculations was obtained. At higher temperatures, measurements and simulations differed noticeably. The importance of C(2) for the growth of carbon clusters was confirmed.

No abstract

The pyrolysis kinetics of CCl(4) behind reflected shock waves was studied with high-repetition-rate time-of-flight mass spectrometry. For modeling, quantum mechanical calculations were performed to evaluate the dissociation energies of CCl bonds for the different CCl(x) (x = 1 to 4) radicals. Good agreement with the JANAF thermochemical table was found. With the reaction mechanism developed for CCl(4) decomposition satisfactory agreement with experimental results was obtained. The investigations show the importance of C(2)Cl(2) formation for understanding the processes of carbon cluster growth leading to carbonaceous particle formation.