Dissociative Ionization and Thermal Decomposition of Cyclopentanone

5 years ago

Dissociative Ionization and Thermal Decomposition of Cyclopentanone

Jordy Bouwman, Andras Bodi, Johan I. M. Pastoors, Patrick Hemberger

Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. The fragmentation of the ions is dominated by loss of CO, C2H4, and C2H5, leading to daughter ions at m/z 56 and 55. Exploring the C5H8O.+ potential energy surface reveals hydrogen tunneling to play an important role in low-energy decarbonylation and probably also in the ethene-loss processes, yielding 1-butene and methylketene cations, respectively. At higher energies, pathways without a reverse barrier open up to oxopropenyl and cyclopropanone cations by ethyl-radical loss and a second ethene-loss channel, respectively. A statistical Rice–Ramsperger–Kassel–Marcus model is employed to test the viability of this mechanism. The pyrolysis of cyclopentanone is studied at temperatures ranging from about 800 to 1100 K. Closed-shell pyrolysis products, namely 1,3-butadiene, ketene, propyne, allene, and ethene, are identified based on their photoion mass-selected threshold photoelectron spectrum. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. A reaction mechanism is derived incorporating both stable and reactive species, which were not predicted in prior computational studies. Unravelling the decomposition of cyclopentanone: With the growing use of renewable fuels, there is a strong need to understand their unimolecular dissociation mechanism. Here, we investigate the decomposition of neutral and cationic cyclopentanone initiated by flash pyrolysis and tuneable vacuum ultraviolet radiation, respectively. The decomposition products (see figure) are isomer-specifically identified by mass-selected TPES and detailed reaction mechanisms are discussed.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201702376