Formation of Smaller Anions from C_nN⁻ (n = 1–3, 5–7) in the Circumstellar Medium

Abstract

We probe a new pathway for the formation of smaller anions from the temporary negative ion states (anion resonances) of C n N− (n = 1–3, 5–7) in the circumstellar envelope of IRC+10216. C n N− (n = 1–3, 5–7) anions were collisionally excited to their resonance states and were observed to decay into a variety of smaller anions. The measured kinetic-energy-release distributions for the anionic fragments arising from each of the parent anions indicate a concerted manner of occurrence of these fragments, implying rich dissociation dynamics. and C2N− were found to be dominant fragments of these anions, suggesting their presence in the external layers of IRC+10216 where UV photons penetrate. C n N− (n = 1–3) were also observed to undergo dissociative and nondissociative double-electron detachments, with the former being dominant. The significance of this new pathway in determining the stability and abundance of anions in IRC+10216 is discussed.

Low-lying Dipole Resonances in FeCN−: A Viable Formation Pathway for FeCN− in Space

“…The presence of anions in the interstellar medium (ISM) was predicted several decades ago (Sarre 1980;Herbst 1981), but only six anions have been detected to date. Anion resonances accessed via electron attachment (Pelc et al 2016) or by excitation of a ground-state anion (Nrisimhamurty et al 2016;Chacko et al 2018Chacko et al , 2020Lietard et al 2021b) are considered to play a vital role in the formation of anions in the ISM. However, the pathways for the formation of anions by electron attachment face restrictions in the low-density ISM where three-body collisions to dispose of the excess energy are not plausible.…”