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Anionic carbonate CO3− has been found in interstellar space and the Martian atmosphere, but its production mechanism is in debate so far. To mimic the irradiation-induced reactions on icy micrograins in the Martian atmosphere and the icy shell of interstellar dust, here we report a laboratory investigation on the dissociative electron attachments to the molecular clusters of CO2. We find that anionic species (CO2)n−1O− and (CO2)n− (n = 2, 3, 4) are produced in the concerted reaction and further stabilized by the evaporative cooling after the electron attachment. We further propose a dynamics model to elucidate their competitive productions: the (CO2)n− yields survive substantially in the molecular evaporative cooling at the lower electron attachment energy, while the reactions leading to (CO2)n−1O− are favored at the higher attachment energy. This work provides new insights into physicochemical processes in CO2-rich atmospheres and interstellar space. [ABSTRACT FROM AUTHOR]

A resonant system consisting of an excess electron and a closed-shell atom or molecule, as a temporary negative ion, is usually in doublet-spin states that are analogous to bright states of photoexcitation of the neutral. However, anionic higher-spin states, noted as dark states, are scarcely accessed. Here, we report the dissociation dynamics of CO− in dark quartet resonant states that are formed by electron attachments to electronically excited CO (a3Π). Among the dissociations to O−(2P) + C(3P), O−(2P) + C(1D), and O−(2P) + C(1S), the latter two are spin-forbidden in the quartet-spin resonant states of CO−, while the first process is preferred in 4Σ− and 4Π states. The present finding sheds new light on anionic dark states. [ABSTRACT FROM AUTHOR]