The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and its Relevance in Solar Geoengineering Models

Ionic Route to Atmospheric Relevant HO2 and Protonated Formaldehyde from Methanol Cation and O2

Gas-phase ion chemistry influences atmospheric processes, particularly in the formation of cloud condensation nuclei by producing ionic and neutral species in the upper troposphere-stratosphere region impacted by cosmic rays. This work investigates an exothermic ionic route to the formation of hydroperoxyl radical (HO2) and protonated formaldehyde from methanol radical cation and molecular oxygen. Methanol, a key atmospheric component, contributes to global emissions and participates in various chemical reactions affecting atmospheric composition. The two reactant species are of fundamental interest due to their role in atmospheric photochemical reactions, and HO2 is also notable for its production during lightning events. Our experimental investigations using synchrotron radiation reveal a fast hydrogen transfer from the methyl group of methanol to oxygen, leading to the formation of CH2OH+ and HO2. Computational analysis corroborates the experimental findings, elucidating the reaction dynamics and hydrogen transfer pathway. The rate coefficients are obtained from experimental data and shows that this reaction is fast and governed by capture theory. Our study contributes to a deeper understanding of atmospheric processes and highlights the role of ion-driven reactions in atmospheric chemistry.

Calculation of electron interaction models in N2 and O2

Cosmic rays have the potential to significantly affect the atmospheric composition by increasing the rate and changing the types of chemical reactions through ion production. The amount and states of ionization, and the spatial distribution of ions produced are still open questions for atmospheric models. To precisely estimate these quantities, it is necessary to simulate particle-molecule interactions, down to very low energies. Models enabling such simulations require interaction probabilities over a broad energy range and for all energetically allowed scattering processes. In this paper, we focus on electron interaction with the two most abundant molecules in the atmosphere, i.e., N2 and O2, as an initial step. A set of elastic and inelastic cross section models for electron transportation in oxygen and nitrogen molecules valid in the energy range 10 eV - 1 MeV, is presented. Comparison is made with available theoretical and experimental data and a reasonable good agreement is observed. Stopping power is calculated and compared with published data to assess the general consistency and reliability of our results. Good overall agreement is observed, with relative differences lower than 6% with the ESTAR database.

Formation of H3O+ and OH by CO2 and N2O trace gases in the atmospheric environment

The impact of cosmic rays' energetic subatomic particles on climate and global warming is still controversial and under debate. Cosmic rays produce ions that can trigger fast reactions affecting chemical networks in the troposphere and stratosphere especially when a large amount of relevant trace gases such as carbon dioxide, methane, sulfur dioxide and water are injected by volcanic eruptions. This work focuses on synchrotron experiments and an ab initio theoretical study of the ion chemistry of carbon dioxide and nitrous oxide radical cations reacting with water. These molecules catalyze a fast exothermic formation of hydronium ions H3O+ and the hydroxyl radical OH, the main oxidant in the atmosphere. Moreover, theoretical calculations demonstrate that at the end of the catalytic cycle, CO2 and N2O are produced vibrationally excited and subsequently they quench in the microsecond time scale by collision with the surrounding atmospheric molecules at the pressure and temperature of the upper-troposphere/stratosphere. The chemistry involved in these reactions has a strong impact on the oxidant capacity of the atmosphere, on the sulfate aerosol production, on the cloud formation and eventually on the chemical networks controlling climate and global warming models.

Perspectives of Gas Phase Ion Chemistry: Spectroscopy and Modeling

The study of ions in the gas phase has a long history and has involved both chemists and physicists. The interplay of their competences with the use of very sophisticated commercial and/or homemade instrumentations and theoretical models has improved the knowledge of thermodynamics and kinetics of many chemical reactions, even if still many stages of these processes need to be fully understood. The new technologies and the novel free-electron laser facilities based on plasma acceleration open new opportunities to investigate the chemical reactions in some unrevealed fundamental aspects. The synchrotron light source can be put beside the FELs, and by mass spectrometric techniques and spectroscopies coupled with versatile ion sources it is possible to really change the state of the art of the ion chemistry in different areas such as atmospheric and astro chemistry, plasma chemistry, biophysics, and interstellar medium (ISM). In this manuscript we review the works performed by a joint combination of the experimental studies of ion–molecule reactions with synchrotron radiation and theoretical models adapted and developed to the experimental evidence. The review concludes with the perspectives of ion–molecule reactions by using FEL instrumentations as well as pump probe measurements and the initial attempt in the development of more realistic theoretical models for the prospective improvement of our predictive capability.

Ion Chemistry of Carbon Dioxide in Nonthermal Reaction with Molecular Hydrogen

The exothermic hydrogen transfer from H₂ to CO₂^·+ leading to H and HCO₂⁺ is investigated in a combined experimental and theoretical work. The experimental mass/charge ratios of the ionic product (HCO₂⁺) and the ionic reactant (CO₂^·+) are recorded as a function of the photoionization energy of the synchrotron radiation. Theoretical density functional calculations and variational transition state theory are employed and adapted to analyze the energetic and the kinetics of the reaction, which turns out to be barrierless and with nonthermal rate coefficients controlled by nonstatistical processes. This study aims to understand the mechanisms and energetics that drive the reactivity of the elementary reaction of CO₂^·+ with H₂ in different processes.

Fabrication of a New, Low-Cost, and Environment-Friendly Laccase-Based Biosensor by Electrospray Immobilization with Unprecedented Reuse and Storage Performances

The fabrication of enzyme-based biosensors has received much attention for their selectivity and sensitivity. In particular, laccase-based biosensors have attracted a lot of interest for their capacity to detect highly toxic molecules in the environment, becoming essential tools in the fields of white biotechnology and green chemistry. The manufacturing of a new, metal-free, laccase-based biosensor with unprecedented reuse and storage capabilities has been achieved in this work through the application of the electrospray deposition (ESD) methodology as the enzyme immobilization technique. Electrospray ionization (ESI) has been used for ambient soft-landing of laccase enzymes on a carbon substrate, employing sustainable chemistry. This study shows how the ESD technique can be successfully exploited for the fabrication of a new promising environment-friendly electrochemical amperometric laccase-based biosensor, with storage capability up to two months without any particular care and reuse performance up to 63 measurements on the same electrode just prepared and 20 measurements on the one-year-old electrode subjected to redeposition. The laccase-based biosensor has been tested for catechol detection in the linear range 2-100 μM, with a limit of detection of 1.7 μM, without interference from chrome, cadmium, arsenic, and zinc and without any memory effects.

VUV Photofragmentation of Chloroiodomethane: The Iso-CH2I-Cl and Iso-CH2Cl-I Radical Cation Formation

Dihalomethanes XCH₂Y (X and Y = F, Cl, Br, and I) are a class of compounds involved in several processes leading to the release of halogen atoms, ozone consumption, and aerosol particle formation. Neutral dihalomethanes have been largely studied, but chemical physics properties and processes involving their radical ions, like the pathways of their decomposition, have not been completely investigated. In this work the photodissociation dynamics of the ClCH₂I molecule has been explored in the photon energy range 9–21 eV using both VUV rare gas discharge lamps and synchrotron radiation. The experiments show that, among the different fragment ions, CH₂I⁺ and CH₂Cl⁺, which correspond to the Cl- and I-losses, respectively, play a dominant role. The experimental ionization energy of ClCH₂I and the appearance energies of the CH₂I⁺ and CH₂Cl⁺ ions are in agreement with the theoretical results obtained at the MP2/CCSD(T) level of theory. Computational investigations have been also performed to study the isomerization of geminal [ClCH₂I]^•+ into the iso-chloroiodomethane isomers: [CH₂I–Cl]^•+ and [CH₂Cl–I]^•+.