Learn more. 0.1 %), secondary reactions initiated by atomic hydrogen may have a small contribution to the formation of the observed products, or isomerization thereof. In the photoionization mass spectra reported by Chambreau et al.,37 products are also seen in the mass channels corresponding to vinylacetylene (C4H4) and vinyl (C2H3). The formation of cyclopentenone+H2 was computed to be one of the lowest energy pathways for dissociation of cyclopentanone (Figure 7) and its subsequent dissociation through α‐, β‐, and γ‐cleavage is summarized in Figure 8. Reaction coordinates were scanned at the B3LYP/6‐311++G(d,p) level of theory to locate transition states and intermediates. Your Request For Quotation has been forwarded to Spectrum's chemical manufacturing group for evaluation and pricing. It's an organic compound and a cyclic ketone that most often used as a fragrance. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. Reactive product species, such as ketene and a number of radicals, have been sampled directly from the reactor and have been identified unambiguously. Please use a different name, or choose one from the list. Atomic hydrogen is abundantly formed according to the proposed cyclopentanone dissociation mechanism and, although the density of the parent molecule in the reactor is kept low (ca. Wavy arrows indicate tunneling contributions in hydrogen‐transfer isomerization steps. Normalized threshold photoelectron spectra (TPES) of fragments m/z 84, 54, 42, 41, 40, 39, 28, and 15 recorded at 920 K over a photon energy range of 8 to 11 eV in steps of 0.05 eV. Normalized integrated ion signals as a function of pyrolysis tube temperature for the parent and prominent closed‐shell pyrolysis products. Thus, understanding the dissociative photoionization mechanism is important, because the onset of dissociative ionization can be shifted towards lower photon energies at elevated temperatures, which may be wrongly assigned to decomposition upon pyrolyis.40, 41 In addition, similar fragmentation connects both the neutral molecules’ and ions’ potential energy surface, which can be used to derive heats of formation of reactive intermediates in the absence of a reverse barrier.42 It is also interesting to note an important difference between dissociative photoionization process and pyrolysis mechanisms. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. One of numerous possible classes of biofuel molecules are ketones. Supplementary pyrolysis reaction mechanisms are proposed to explain some of the observed products. Open symbols represent experimentally measured values and continuous lines correspond to the RRKM model result. Cyclopentanone found in: Cyclopentanone, Cyclopentanone, Cyclopentanone p-Toluenesulfonylhydrazone, Cyclopentanone Oxime, CYCLOPENTANONE AT 1000 UG/ML.. However, their formation has neither been predicted computationally previously, nor were these species detected experimentally before.9, 11 Ketene and allene may be formed from diradicals that form through the α‐, β‐, or γ‐cleavage of cyclopentanone as shown in Figure 8, analogous to the unimolecular decomposition of cyclohexanone.10 Both α‐ and β‐cleavage may yield ketene. Lastly, a noticeable difference lies in the CO‐loss channel. Porterfield et al.10 found that keto–enol tautomerization followed by a retro Diels–Alder fragmentation is responsible for the formation of CH2=C(OH)−CH=CH2+C2H4. The detection of a very weak signal at m/z 83 indicates that keto–enol tautomerization only plays a minor role in dissociative photoionization. Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Cyclopentanone pyrolysis products are compared to those predicted in a previous computational study to pin down the underlying dissociation mechanism. The sample expanded into the source chamber, which was maintained at about 1×10−4 mbar. The multiplexed nature of ms‐TPES offers a clear advantage over the use of FTIR matrix isolation spectroscopy to assign products; spectral information is obtained mass selectively and isomer specific identification of the products are readily made.22 The detection of the first generation of species from the reactor reveals the true underlying chemical mechanism and supplies crucial information that is needed for modeling the combustion of biofuels. 5 Related Records Expand this section. The detection of propargyl could point to cyclopentenone also being an intermediate species in ketene formation. The barrier involved in this reaction is located at 325.1 kJ mol−1.11 Alternatively, α‐cleavage of cyclopentanone followed by an isomerization was calculated to result in the same products, albeit at a lower rate. Furthermore, single‐photon dissociative ionization data employing parent‐ion internal energy selection are not available. In this work, we find that this channel is significantly higher (by 0.2 eV) in energy at 1.97 eV with respect to the cation (11.26 eV w.r.t. Time‐of‐flight mass spectrum of cyclopentanone pyrolysis products formed at about 1100 K and ionized at 10.5 eV constructed from coincidences of all photoelectrons regardless of their position on the detector (i.e., energy) with photoions. Due to the strong transition at 10.5 eV, the m/z 28 is assigned to ethylene.34 Carbon monoxide could contribute to this mass channel as well, but its ionization threshold is 14.01 eV,35 beyond the photon energy range of this study. While fossil fuels are typically composed of mostly carbon and hydrogen, biofuels also contain oxygen in the form of hydroxyl (e.g., ethanol), carboxyl, aldehyde, or ketone functional groups.2 Their varying composition leads to differing combustion chemistry, which needs to be thoroughly understood. The hydrogen‐atom tunneling rate constants in CO loss were calculated using an Eckart barrier,20 and only the transition state transitional mode frequencies were fitted in the high‐energy C2H4 and C2H5 loss, together with the critical tunneling frequency in CO‐loss. Since the CO‐loss and the low‐energy C2H4‐loss channel are expected to behave rather similarly with the former being the more dominant one, we have not explicitly considered the latter in the model. Hydrogen migration as a potential driving force in the thermal decomposition of dimethoxymethane: New insights from pyrolysis imaging photoelectron photoion coincidence spectroscopy and computations. Mass spectra provide data for structural assessments, fragmentation being performed by semi-empirical rules serving to the study of unknown compounds. When studying dissociative photoionization processes, the threshold ionization fractional parent and daughter ion abundances were plotted in the breakdown diagram, which often contains clues as to the fragmentation mechanism,46 and can be modeled quantitatively using statistical thermodynamics approaches to determine accurate dissociative photoionization thresholds.47 Furthermore, owing to the long acceleration region and low extraction field, it took several microseconds for the photoions to reach their terminal velocity in the mass spectrometer. The time‐of‐flight distributions, shown in Figure 2 B, shed light on the competition between the 28 and 29 amu loss channels. This is much lower than the direct C−H bond breaking dissociative photoionization energy (11.42 eV), which implies isomerization to the enolic parent ion, which subsequently may lose a hydrogen atom already at 10.32 eV, making this the lowest energy dissociative photoionization process discussed herein.