On the formation of cyclopentadiene in the C₃H₅˙ + C₂H₂ reaction

Abstract

The reaction between the allyl radical (C3H5˙) and acetylene (C2H2) in a heated microtubular reactor has been studied at the VUV beamline of the Swiss Light Source. The reaction products are sampled from the reactor and identified by their photoion mass-selected threshold photoelectron spectra (ms-TPES) by means of imaging photoelectron photoion coincidence spectroscopy. Cyclopentadiene is identified as the sole reaction product by comparison of the measured photoelectron spectrum with that of cyclopentadiene. With the help of quantum-chemical computations of the C5H7 potential energy surface, the C2H2 + C3H5˙ association reaction is confirmed to be the rate determining step, after which H-elimination to form C5H6 is prompt in the absence of re-thermalization at low pressures. The formation of cyclopentadiene as the sole product from the allyl + acetylene reaction offers a direct path to the formation of cyclic hydrocarbons under combustion relevant conditions. Subsequent reactions of cyclopentadiene may lead to the formation of the smallest polycyclic aromatic molecule, naphthalene.

Nitrogen matters: the difference between PANH and PAH formation

“…This approach has been used in the identification and characterization of elusive reactive intermediates, 28 which help unveil complex reaction mechanisms in diverse reactive environments. [29][30][31] Ab initio calculations and kinetic modeling are performed to explore the potential energy surface and rationalize the experimental data. 32 Contrary to our expectations, based primarily on naphthalene formation in the analogous phenyl + vinylacetylene reaction, 23 we did not detect quinoline and argue that it may only be a minor reaction product.…”

Dissociative Ionization and Thermal Decomposition of Cyclopentanone

“…The dissociative photoionization of cyclopentanone has been studied to distinguish dissociative ionization products from thermal decomposition products . Furthermore, it is interesting to compare and contrast the fragmentation processes in the neutral molecule, induced by heat in the microreactor, and in the ion, brought about by the excess energy of an ionizing vacuum ultraviolet (VUV) photon.…”

“…or, alternatively, through thermal dissociation of allyl followed by ionization [Eqs. ] …”

Gas-phase infrared spectroscopy of the rubicene cation (C26H14•+)

“…Although, some success is reported for observations on Tu Tau; a binary star system hosting a carbon-rich AGB star and a blue companion (Buss et al 1991;Speck & Barlow 1997;Boersma et al 2006). Knowledge available from the combustion community has been used to explain the bottom-up formation of PAHs in the outflows of such stars (e.g., Frenklach & Feigelson 1989;Cherchneff et al 1992) and suggests that pentagon-containing PAH species are also produced (Bouwman et al 2015;Johansson et al 2018;Schulz et al 2019;McCabe et al 2020). Inclusion of pentagons can also be achieved through top-down erosion of large aromatic species, which is considered the prime mechanism for creating fullerenes (Berné & Tielens 2012).…”

“…A large variety of mechanisms are expected to contribute to the formation of PAHs in the combustion of fossil fuels (Richter & Howard 2000;Moriarty & Frenklach 2000;Parker et al 2014;Kaiser et al 2015;Yang et al 2017), some of which are applied to astrochemistry to explain the formation of interstellar aromatic molecules in the outflows of carbon-rich stars (e.g., Frenklach & Feigelson 1989;Cherchneff et al 1992). The sequences of chemical reactions involved not only produce clean hexagon containing aromatic molecules, but they have also been shown in the laboratory to result in pentagon containing species (Bouwman et al 2015;Johansson et al 2018;Commodo et al 2019;Schulz et al 2019;McCabe et al 2020). Pentagon inclusion is also invoked to explain the formation of fullerenes through erosion of large PAHs as this provides a way to bowl the planar PAH plane (Berné & Tielens 2012).…”