Using isotopologues to probe the potential energy surface of reactions of C2H2 ++C3H4

To form or not to form a reaction complex: exploring ion-molecule reactions between C3H4 isomers and Xe+ and O2. Faraday Discuss 2024. [PMID: 38764353 DOI: 10.1039/d4fd00005f]

Ion-molecule reactions are an essential contributor to the chemistry of a diverse range of environments. While a great deal of work has been done to understand the fundamental mechanisms driving these reactions, there is still much more to discover. Here, we expand upon prior studies on ion-molecule reactions involving two isomers of C3H4, allene (H2C3H2) and propyne (H3C3H). Specifically, we probe the previously observed isomeric dependent reactivity of these molecules by reacting them with two ions with nearly identical ionization potentials, Xe+ and O2+. Our goal is to determine if the isomer-dependent reaction mechanisms previously observed are universal for C3H4 or if they depend on the ion character as well. Through the combination of experimental measurements and theoretical calculations, we found that both isomeric structure and identity of the ion contribute to the propensity of a reaction complex forming or for only long-range charge transfer to occur.

Cold Ion-Molecule Reactions in the Extreme Environment of a Coulomb Crystal

Coulomb crystals provide a unique environment in which to study ion-neutral gas-phase reactions. In these cold, trapped ensembles, we are able to study the kinetics and dynamics of small molecular systems. These measurements have connections to chemistry in the Interstellar Medium (ISM) and planetary atmospheres. This Feature Article will describe recent work in our laboratory that uses Coulomb crystals to study translationally cold, ion-neutral reactions. We provide a description of how the various affordances of our experimental system allow for detailed studies of the reaction mechanisms and the corresponding products. In particular, we will describe quantum-state resolved reactions, isomer-dependent reactions, and reactions with a rarely studied, astrophysically relevant ion, CCl+.

Reactions of Acetonitrile with Trapped, Translationally Cold Acetylene Cations

The reaction of the acetylene cation (C₂H₂⁺) with acetonitrile (CH₃CN) is measured in a linear Paul ion trap coupled to a time-of-flight mass spectrometer. C₂H₂⁺ and CH₃CN are both noted for their astrochemical abundance and predicted relevance for understanding prebiotic chemistry. The observed primary products are c-C₃H₃⁺, C₃H₄⁺, and C₂NH₃⁺. The latter two products react with excess CH₃CN to form the secondary product C₂NH₄⁺, protonated acetonitrile. The molecular formula of these ionic products can be verified with the aid of isotope substitution via deuteration of the reactants. Primary product reaction pathways and thermodynamics are investigated with quantum chemical calculations and demonstrate exothermic pathways to two isomers of C₂NH₃⁺, two isomers of C₃H₄⁺, and the cyclopropenyl cation c-C₃H₃⁺. This study deepens our understanding of the dynamics and products of a pertinent ion-molecule reaction between two astrochemically abundant molecules in conditions that mimic those of the interstellar medium.