Production of Long-Lived Benzene Dications from Electron Impact in the 20–2000 eV Energy Range Combined with the Search for Global Minimum Structures

Abstract

In this work, we report a systematic search of metastable C6H n 2+ (n = 1–6) dications from electron impact time-of-flight measurements of several benzene derivatives in combination with global minimum search based on the genetic algorithm. Our theoretical calculations reveal that the C6H n 2+ (n < 6) global minimum structures are completely different from that of the benzene dication, featuring linear carbon chains and/or cyclopropenylium moieties. Experimentally, the doubly charged species were investigated for a wide range of electron impact energies, from 20 to 2000 eV, for benzene and several monosubstituted compounds containing either electron-withdrawing or -donating groups. Furthermore, the C6H n 2+ production, evaluated from the yields of the dications with respect to that of the parent ion (or parent dication), was compared to those obtained from charge exchange in the doubly charged 2E spectra and electron impact experiments available in the literature. The yields of the long-lived benzene dications were contrasted to those analogues formed in chlorobenzene. Moreover, the formation of C6H n 2+ species is strongly dependent on the nature of substituent groups, with electron-withdrawing ones favoring the dication formation.

Bimolecular reactions of CH2CN2+ with Ar, N2 and CO: reactivity and dynamics

“…Here we can directly analogise with the benzene dication which has a number of metastable minima on the dicationic potential energy surface which are sampled by C 6 H 6 2+ ions. [101][102][103] The six metastable dication states revealed by the calculations (Table 4) have adiabatic double ionization potentials, from CH 2 CN, of between 28.9 eV and 32.9 eV. These double ionization potentials are significantly lower than the double ionization potentials of Ar (43.39 eV), 104 N 2 (B43 eV), [105][106][107] and CO (B41.5 eV).…”

“…Here we can directly analogise with the benzene dication which has a number of metastable minima on the dicationic potential energy surface which are sampled by C 6 H 6 2+ ions. 101–103…”

Why an integrated approach between search algorithms and chemical intuition is necessary?

“…It is important to note that AUTOMATON is a program that uses a probabilistic cellular automated method to generate the initial population, which then evolves through genetic operations. This method has been designed to identify the global minimum, assessing its efficiency in different systems, 41 with recent application to design global minima with planar hypercoordinate carbons, [49][50][51][52] organic dications, 53 deltahedral Zintl clusters, 54 among others. 55,56 Our initial search yielded 1450 different geometries.…”

Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy, and implications in AGN environments

“…In addition to fragmentation processes, the ionisation of small cycles, including aromatic rings, can induce molecular isomerisation (Jašík et al 2015;Monfredini et al 2016;Fantuzzi et al 2018;Quitián-Lara et al 2018;Monfredini et al 2019;Fantuzzi et al 2019;Wolff et al 2020), which is usually accompanied by a severe loss of molecular integrity. Several examples were demonstrated by screening the potential energy surface (PES) of a given molecular structure for each charge state under consideration (Jašík et al 2015;Fantuzzi et al 2018;Gutsev et al 2020;Hendrix et al 2020;Cerqueira et al 2020).…”