Investigating Possible Dipole-Bound States of Cyanopolyynes: the Case for the C5 N- Anion Detected in Interstellar Space

Abstract

We present results of quantum structure calculations aimed at demonstrating the possible existence of dipole-bound states (DBS) for the anion C5N-${{\rm{C}}_5 {\rm{N}}^ - }$ , a species already detected in the Interstellar medium (ISM). The positive demonstration of DBS existence using ab initio studies is an important step toward elucidating possible pathways for the formation of the more tightly bound valence bound states (VBS) in environments where free electrons from starlight ionization processes are known to be available to interact with the radical partner of the title molecule. Our current calculations show that such excited DBS states can exist in C5N-${{\rm{C}}_5 {\rm{N}}^ - }$ , in agreement with what we had previously found for the smallercyanopolyyne in the series: the C3N-${{\rm{C}}_3 {\rm{N}}^ - }$ anion. This system has a very weakly bound anion with binding energies of about 3 and 9 cm-1 for the 1Σ+${^1 \Sigma ^ + }$ and 3Σ+${^3 \Sigma ^ + }$ DBS, respectively.