Detecting combustion intermediates via broadband chirped-pulse microwave spectroscopy

Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm

“…The experimental aspect of the present effort involves direct detection and quantification of a number of the key acetone pyrolysis reaction products that emerge from a silicon carbide (SiC) microreactor. ,, We use Chirped-Pulse Fourier Transform rotational spectroscopy , in the millimeter-wave region (CP-FTmmW). , Since the frequencies of rotational transitions principally depend on the molecular carrier’s three moments of inertia, rotational spectroscopy achieves chemical specificity, distinguishing between isotopologues, isomers, and conformers . Because CP-FTmmW spectroscopy involves multiplexed detection and simultaneously samples ∼10 4 spectral resolution elements, it is ideal for detection of transitions that belong to multiple chemical species. , In addition, transitions observed using CP-FTmmW spectroscopy maintain meaningful relative intensities. , This intensity information can then be converted into relative abundances of observed compounds. − An additional feature of the SiC reactor is the short observation times (25–150 μs), which facilitates direct access to the nascent steps involved in pyrolytic processes at high temperatures. These key aspects are utilized here to study reaction kinetics and dynamics in a flash pyrolysis reactor …”

Combustion, Chemistry, and Carbon Neutrality

“…Among further techniques that are relatively new to combustion diagnostics, microwave spectroscopy with its superb resolution is particularly suited for the sensitive detection of polar molecules such as oxygenated intermediates. , In a first exploratory study, flame samples from a dimethyl ether (DME) and an ethene flame were analyzed, and species profiles of CH 2 O and CH 3 CHO were determined that compared well with EI-MBMS experiments . Significant improvements were recently reported that were made possible by using broadband chirped-pulse microwave spectroscopy; Figure shows the high quality of the resulting spectra …”

“…Unique identification capabilities of broadband microwave spectroscopy is shown by identification of (a) the 2 1,1 –2 1,2 transition of dimethyl ether, (b) the 2 1,1 –2 1,2 transition of formaldehyde, (c) the 1 0,1 –0 0,0 transition of formic acid anhydride, and (d) the 2 1,2 –1 1,1 transition of formic acid anhydride after sampling from reactive mixtures . Reproduced with permission from ref . Copyright 2020 The Combustion Institute, published by Elsevier.…”

“…221 Significant improvements were recently reported that were made possible by using broadband chirped-pulse microwave spectroscopy; Figure 10 shows the high quality of the resulting spectra. 222 For this analysis, gas samples were withdrawn from reactive atmospheres of DME and dimethoxy methane (DMM), respectively, with oxygen, diluted in argon and supersonically expanded into the high vacuum of the microwave spectrometer, where the cooled molecules were subjected to the chirped pulses. 222 Strong-field coherence breaking was demonstrated as a feasible procedure to aid assignment of spectral structures.…”

“…222 Strong-field coherence breaking was demonstrated as a feasible procedure to aid assignment of spectral structures. 222 The technique is not yet mature for application in combustion systems, but it offers potential for the unambiguous assignment of oxygenated intermediates of which a large number of different molecular structure can be involved in oxidation reactions (see also Figure 8).…”