SIMBAD references

In this paper, we report results of an extensive theoretical study on MgC₄H chains conducted at DFT and CCSD(T) levels motivated by the recent discovery of this species in IRC+10216. A detailed characterization of both neutral and charged species is presented, which include structural, chemical bonding and vibrational properties, rotational, centrifugal distortion and Watson l-type doubling constants, dipole moments, Fermi contact, and spin-rotation constants. In addition, we present ab initio estimates needed for subsequent astrochemical evolution modelling (e.g. dissociation energies, acidity, electron attachment, and ionization energies and related chemical reactivity indices). Possible formation pathways are also discussed. They comprise exchange, (radiative) association, dissociative recombination, and ion neutralization reactions. As an important result aiming at stimulating further observational searching, we suggest that MgC₄H^– anions should also be observable via rovibrational spectroscopy. The reason is twofold: (i) Neutral MgC₄H⁰ chains possess a sufficiently large dipole moment consistent with dipole-bound anion states and large electron attachment cross-sections. (ii) MgC₄H^– anions possess a dipole substantially larger than MgC₄H⁰ neutrals (and also larger than that estimated earlier for the longest astronomically detected C₈H^– anion). This makes MgC₄H^– anion intensities in rovibrational spectrum experimentally accessible even in the unlikely case of a relative abundance MgC₄H^–/MgC₄H⁰ comparable to that of CH₄, whose anion has the lowest relative abundance observed so far in space because weakly polar C₄H⁰ chains do not support dipole-bound anion states. A suggestion on why, counterintuitively, the MgC₂H abundance found in IRC+10216 was lower than that of the longer MgC₄H is also presented.