Experimental and theoretical studies of reactions between H atoms and carbanions of interstellar relevance

Abstract

The recent detection of molecular anions in the interstellar medium (ISM) has highlighted the need for laboratory studies of negative ion chemistry. Hydrogen atoms are the most abundant atomic species in the ISM, and the chemistry of H atoms with anions may contribute to molecular synthesis in interstellar clouds. This work is a combined experimental and computational study of a series of anions reacting with H atoms by associative detachment (A- + H → AH + e-). The anions include deprotonated nitriles (CH2CN-, CH3CHCN-, and (CH3)2CCN-), acetaldehyde (HC(O)CH 2-), acetone (CH3C(O)CH2-), ethyl acetate (CH3CH2OC(O)CH 2-), methanol (CH3O-), and acetic acid (CH3CO2-). Experimental measurements of the reaction rate constants were made with the flowing afterglow-selected ion flow tube technique. Ab initio theoretical calculations were carried out to explore the reaction mechanism and investigate the factors influencing reaction efficiencies, which are largely proportional to reaction exothermicities. Other factors influencing reaction efficiencies include the charge density on the reactive site of the anion, the characteristics of the potential energy surfaces along the approach of the reactants, and angular momentum conservation of the anion-H atom collision. © 2010. The American Astronomical Society.