Experimental and Computational Studies of the Reactions of N and O Atoms with Small Heterocyclic Anions

The existence of heterocyclic aromatic anions in extraterrestrial environments, such as the upper atmosphere of Titan, has been recently confirmed by data from the Cassini spacecraft. Nitrogen and oxygen atoms are also common species in the ionospheres of planets and moons and in the interstellar medium. In the current work, we extend previous studies to explore the reactivity of five-membered ring aromatic anions that contain nitrogen, oxygen, or sulfur (deprotonated pyrrole, furan, and thiophene) with N and O atoms both experimentally and computationally. Furanide and thiophenide anions react with the N atom by associative electron detachment (AED). All three anions react with the O atom both by AED and by processes that form ionic products. The reaction of pyrrolide anion with the O atom generates only one ionic product C4H3NO-, corresponding to an O addition and H loss process. The corresponding process is observed as the major channel for the reaction of furanide anion with the O atom while other ionic products HCOO- and C2H- are also formed. The reaction of thiophenide with the O atom is more complex, and four ionic products are generated, of which three are sulfur-containing ions. The reaction mechanisms are studied theoretically by employing density functional theory calculations, and, spin conversion is found to be critical for understanding some product distributions. This work provides insight into the rich gas-phase chemistry of aromatic ion atom reactions, which are relevant to ionospheric and interstellar chemistry.