Gas-Phase Reactions of Deprotonated Nucleobases with H, N, and O Atoms.

Complex organic molecules, the hallmark of terrestrial life, are increasingly detected in exotic environments throughout the universe. Our studies probe the ion chemistry of these biomolecules. We report gas-phase reaction rate constants for five deprotonated nucleobases (adenine, cytosine, guanine, thymine, and uracil) reacting with the atomic species H, N, and O. Hydrogen atoms react at moderate rates via associative electron detachment. Oxygen atom reactions occur more rapidly, generating complex product distributions; reaction pathways include associative electron detachment, substitution of the hydrogen atom by an oxygen atom, and generation of OCN. Nitrogen atoms do not react with the nucleobase anions. The reaction thermodynamics were investigated computationally, and reported product channels are exothermic. Many of the proposed products have been observed in various astrochemical environments. These reactions provide insight into chemical processes that may occur at the boundaries between diffuse and dense interstellar clouds and in complex extraterrestrial ionospheres.