A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface

Abstract

A theoretical study of the reaction of O ( 3 P) with an allyl radical C 3 H 5 J. Chem. Phys. 119, 8966 (2003) The fragmentation mechanisms of the naphthalene molecular ion to [M-+ were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)'s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)'s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0-18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Zand E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H 2 molecule in a two-step fragmentation. H• loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C 4 H 2 ) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%-100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M-C 2 H 2 ] +• structure is the phenylacetylene cation. C 2015 AIP Publishing LLC. [http://dx

Threshold Dissociation of the 1-ethynylpyrene Cation at Internal Energies Relevant to H i Regions

“…The energy necessary for the dissociation of an aromatic CH bond in a PAH cation is higher than the barrier to the migration of an H atom and the formation of an aliphatic CH 2 group (see examples in Solano & Mayer 2015;Trinquier et al 2017a;Castellanos et al 2018). In 1EtyPyr + , the energy for the dissociation of an aromatic CH bond is 5.17 to 5.42 eV (i.e., the bond-dissociation energy in the absence of a transition state, see the previous paragraph), while the barrier to H migration to the next C atom on the same ring is found to be 3.27 to 3.46 eV.…”

From planes to bowls: Photodissociation of the bisanthenequinone cation

“…Their fragmentation mechanisms are well established for small species, e.g. substituted 1,4-naphthoquinone (Becher et al, 1966;Mari et al, 1966;Stensen and Jensen, 1995;Pan et al, 2008) and substituted anthraquinone (Proctor et al, 1981;Beynon and Williams, 1960). Experimental and theoretical studies of larger quinones have not been described in previous reports. In this work, we study the photodissociation of the large quinone cation (4,.…”

Dissociation of polycyclic aromatic hydrocarbons: molecular dynamics studies

“…Regarding theoretical studies on the dissociation of PAHs, a few static density functional theory (DFT) studies are available [27][28][29], with special focus on the H and H 2 losses [28,29]. To the best of our knowledge, dynamics studies regarding PAH dissociation are scarce.…”