Computational studies of gas phase reactions of carbon chain anions with N and O atoms

Abstract

Experimental studies of gas phase reactions of carbanions with N and O atoms have been reported previously to understand ion chemistry relevant to the interstellar medium. In all cases reactions of anions with O atoms exhibit larger reaction rate constants compared to the corresponding N atom reactions. In addition, the open-shell carbon chain anions exhibit higher reactivities than the corresponding closed-shell species in N atom reactions, whereas similar reactivities were observed for both open and closed-shell anions in O atom reactions. These trends are investigated by the current theoretical study of the reactions of HC_n⁻(n = 2, 4, and 6) and C_n⁻ (n = 2, 4–7) with N and O atoms. Our results indicate that spin-forbidden processes are the probable pathways in reactions of closed-shell anions HC_n⁻ with N atoms, and spin conversion limits the reaction efficiency. In reactions of open-shell anions C_n⁻ with N atoms, about 50% of the collisions may proceed through spin-allowed barrierless pathways, which results in relatively higher reaction efficiencies than for the closed-shell reactions. For reactions of all anions with O atoms, the spin-allowed barrierless pathways are the only channels, such that all reactions occur with very high efficiencies. This work provides a greater understanding of the influence of spin effects on the reactivities of anion reactions involving N and O atoms that may be important in the interstellar medium.