HCnN anions in the ISM: exploring their existence and new paths to anionic carbonitriles for n = 3, 5

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

We present results of quantum structure calculations aimed at demonstrating the possible existence of dipole-bound states (DBS) for the anionC 5 N - ${{\rm{C}}_5 {\rm{N}}^ - }$ , 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 inC 5 N - ${{\rm{C}}_5 {\rm{N}}^ - }$ , in agreement with what we had previously found for the smallercyanopolyyne in the series: theC 3 N - ${{\rm{C}}_3 {\rm{N}}^ - }$ anion. This system has a very weakly bound anion with binding energies of about 3 and 9 cm-1 for the1 Σ + ${^1 \Sigma ^ + }$ and3 Σ + ${^3 \Sigma ^ + }$ DBS, respectively.

Structural properties of possible interstellar valence anions of the series HCnN- (n = 3, 5, 7, 9)

In this contribution we investigate the structural properties of stable anions of small carbon clusters, with one nitrogen and one hydrogen atoms attached to the C-cluster, to surmise their possible existence in the Interstellar Medium (ISM). Many possible configurational (geometrical) isomers with positive vertical electron detachment values are presented, and arranged according to their relative energy. Specific attention is paid to the structures of the lowest-energy valence isomers, the chain-structures of HC₇N^- and HC₉N^- anions with quasilinear and linear geometry, respectively. They exhibit relatively large permanent dipole moments (2.697 and 5.034 Debye) and adiabatic electron affinities (AEAs) of 1.13 and 1.35 eV. Isomers of the HNC_n^- family and many branched structures are possible stable species viable for detection in the ISM.

Discovery of two new magnesium-bearing species in IRC+10216: MgC3N and MgC4H

We report on the detection of two series of harmonically related doublets in IRC +10216. From the observed frequencies, the rotational constant of the first series is B = 1380.888 MHz and that of the second series is B = 1381.512 MHz. The two series correspond to two species with a 2Σ electronic ground state. After considering all possible candidates, and based on quantum chemical calculations, the first series is assigned to MgC3N and the second to MgC4H. For the latter species, optical spectroscopy measurements support its identification. Unlike diatomic metal-containing molecules, the line profiles of the two new molecules indicate that they are formed in the outer layers of the envelope, as occurs for MgNC and other polyatomic metal-cyanides. We also confirm the detection of MgCCH that was previously reported from the observation of two doublets. The relative abundance of MgC3N with respect to MgNC is close to one while that of MgC4H relative to MgCCH is about ten. The synthesis of these magnesium cyanides and acetylides in IRC +10216 can be explained in terms of a two-step process initiated by the radiative association of Mg+ with large cyanopolyynes and polyynes followed by the dissociative recombination of the ionic complexes.