Total Electron Detachment and Induced Cationic Fragmentation Cross Sections for Superoxide Anion (O2-) Collisions with Benzene (C6H6) Molecules.

Carlos Guerra,Sergio Díaz-Tendero,Ana I Lozano,Mónica Mendes,Juan C Oller,Paulo Limão-Vieira,Gustavo García,Sarvesh Kumar,Fernando Aguilar-Galindo

doi:10.3390/ijms23031266

Abstract

In this study, novel experimental total electron detachment cross sections for O2− collisions with benzene molecules are reported for the impact energy range (10–1000 eV), as measured with a transmission beam apparatus. By analysing the positively charged species produced during the collision events, relative total ionisation cross sections were derived in the incident energy range of 160–900 eV. Relative partial ionisation cross sections for fragments with m/z ≤ 78 u were also given in this energy range. We also confirmed that heavier compounds (m/z > 78 u) formed for impact energies between 550 and 800 eV. In order to further our knowledge about the collision dynamics governing the fragmentation of such heavier molecular compounds, we performed molecular dynamics calculations within the framework of the Density Functional Theory (DFT). These results demonstrated that the fragmentation of these heavier compounds strongly supports the experimental evidence of m/z = 39–42, 50, 60 (u) cations formation, which contributed to the broad local maximum in the total ionisation observed from 550 to 800 eV. This work reveals the reactivity induced by molecular anions colliding with hydrocarbons at high energies, processes that can take place in the interstellar medium under various local conditions.

Highlights

Benzene is one of the simplest and more stable aromatic ring molecules
If we compare these results with our recent measurements for O2− collisions with N2 [17], we see that the average magnitude of the total electron detachment cross sections (TEDCS) in the common energy range (50–1000 eV) is in concordance with their respective molecular masses, i.e., 3–4 times higher for benzene than for nitrogen
According to the present theoretically predicted ionization and further fragmentation patterns, this local maximum mainly formed by the fragmentation of the heavier adducts formed by the aggregation model we previously proposed in Ref. [16]: a sudden double ionization of benzene and the subsequent electrostatic attraction between the dication and the anion formed a stable covalently bonded C6H6O2+ molecule, which evolved towards the formation of benzene– diol conformers

Summary

Introduction

Benzene is one of the simplest and more stable aromatic ring molecules. It has been considered a prototype for the study of chemical reactions involving biomolecules, such as pyridine [1] and carbamates [2], a building block for the synthesis of carbon nano-cages [3] and a precursor of hydrocarbon structures (e.g., phenol, toluene, aniline, anthracene) with important technological applications [4]. We recently reported an experimental and theoretical analysis of the total electron scattering cross section (TCS) with the aim of providing some reference data for modelling procedures connected with these applications [11]. Additional experimental information on the induced cationic fragmentation, i.e., positively charged fragments with a mass-tocharge ratio (m/z) less than 78 u, is given in terms of relative cross sections normalized to that of the parent ion formation with uncertainty limits within 10 and 20%. These relative fragmentation probabilities were obtained by means of molecular dynamics calculations carried out in the framework of the density functional (DFT) theory.

Methods

Results

Discussion

Conclusion