Using quantum chemical methods, we investigate the possible outcomes of H- reactions with acetylene and diacetylene molecules. We find both reactions to be exothermic reactions without barriers, yielding stable anions of the corresponding polyynes: C2H- and C4H-.We show in this work that the computed chemical rates in the case of the formation of the C4H- anion would be larger than those existing for the direct radiative electron attachment (REA) process, the main mechanism generally suggested for their formation. In the case of the C2H- anion, however, the present chemical rates of formation at low T?are even lower than those known for its REA process, both mechanisms being inefficient for its formation under astrochemical conditions. The present results are discussed in view of their consequences on the issue of the possible presence of such anions in the ISM environments. They clearly indicate the present chemical route to C2H- formation to be inefficient at the expected temperatures of a dark molecular cloud, whereas this is found not to be the case for the C4H-, in line with the available experimental findings. © 2016. The American Astronomical Society. All rights reserved.
EXPLORING A CHEMICAL ROUTE for the FORMATION of STABLE ANIONS of POLYYNES [CnH- (n = 2, 4)] in MOLECULAR CLOUDS
PALAZZETTI, FEDERICO;
2016
Abstract
Using quantum chemical methods, we investigate the possible outcomes of H- reactions with acetylene and diacetylene molecules. We find both reactions to be exothermic reactions without barriers, yielding stable anions of the corresponding polyynes: C2H- and C4H-.We show in this work that the computed chemical rates in the case of the formation of the C4H- anion would be larger than those existing for the direct radiative electron attachment (REA) process, the main mechanism generally suggested for their formation. In the case of the C2H- anion, however, the present chemical rates of formation at low T?are even lower than those known for its REA process, both mechanisms being inefficient for its formation under astrochemical conditions. The present results are discussed in view of their consequences on the issue of the possible presence of such anions in the ISM environments. They clearly indicate the present chemical route to C2H- formation to be inefficient at the expected temperatures of a dark molecular cloud, whereas this is found not to be the case for the C4H-, in line with the available experimental findings. © 2016. The American Astronomical Society. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
