Issue 6, 2022

On the absolute photoionization cross section and threshold photoelectron spectrum of two reactive ketenes in lignin valorization: fulvenone and 2-carbonyl cyclohexadienone

Abstract

We report the absolute photoionization cross section (PICS) of fulvenone and 2-carbonyl cyclohexadienone, two crucial ketene intermediates in lignin pyrolysis, combustion and organic synthesis. Both species were generated in situ by pyrolyzing salicylamide and dectected via imaging photoelectron photoion coincidence spectroscopy. In a deamination reaction, salicylamide loses ammonia yielding 2-carbonyl cyclohexadienone, a ketoketene, which further decarbonylates at higher pyrolysis temperatures to form fulvenone. We recorded the threshold photoelectron spectrum of the ketoketene and assigned the ground state ([X with combining tilde]+2A′′ ← [X with combining tilde]1A′) and excited state (Ã+2A′ ← [X with combining tilde]1A′) bands with the help of Franck–Condon simulations. Adiabatic ionization energies are 8.35 ± 0.01 and 9.19 ± 0.01 eV. In a minor reaction channel, the ketoketene isomerizes to benzpropiolactone, which decomposes subsequently to benzyne by CO2 loss. Potential energy surface and RRKM rate constant calculations agree with our experimental observations that the decarbonylation to fulvenone outcompetes the decarboxylation to benzyne by almost two orders of magnitude. The absolute PICS of fulvenone at 10.48 eV was determined to be 18.8 ± 3.8 Mb using NH3 as a calibrant. The PICS of 2-carbonyl cyclohexadienone was found to be 21.5 ± 8.6 Mb at 9 eV. Our PICS measument will enable the quantification of reactive ketenes in lignin valorization and combustion processes using photoionization techniques and provide advanced mechanistic and kinetics insights to aid the bottom-up optimization of such processes.

Graphical abstract: On the absolute photoionization cross section and threshold photoelectron spectrum of two reactive ketenes in lignin valorization: fulvenone and 2-carbonyl cyclohexadienone

Supplementary files

Article information

Article type
Paper
Submitted
13 11 2021
Accepted
12 1 2022
First published
26 1 2022
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2022,24, 3655-3663

On the absolute photoionization cross section and threshold photoelectron spectrum of two reactive ketenes in lignin valorization: fulvenone and 2-carbonyl cyclohexadienone

Z. Pan, A. Bodi, J. A. van Bokhoven and P. Hemberger, Phys. Chem. Chem. Phys., 2022, 24, 3655 DOI: 10.1039/D1CP05206C

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