Formation of adducts of C_6H with Na^+, Mg^+ and Al^+ metal cations by radiative association

Abstract

The Mg-bearing cations MgC₄H⁺, MgC₆H⁺, MgC₃N⁺, and MgC₅N⁺ have been recently observed in the carbon-rich envelope IRC\,+10216. These species are thought to form upon radiative association between Mg⁺ and the corresponding neutral radical. This work aims to determine the radiative association rate coefficients for the cations Al⁺, Mg⁺, and Na⁺ reacting with carbon chain radicals to estimate the relative importance of metal-bearing carbon cations for each of these metals. For this purpose we use statistical methods in combination with highly accurate ab initio calculations to obtain the radiative association rate coefficient. Moreover, anisotropic effects beyond mono-dimensional capture model are considered, providing a more reliable description of the simulated processes.} The radiative association rate coefficients to form Mg-, Al- and Na-C₆H⁺, as well as MgC₄H⁺, MgC₃N⁺, and MgC₅N⁺, are calculated with the new restrictions considered in this work. These new rate coefficients are included in a chemical model of the C-rich AGB envelope IRC\,+10216. The abundances of MgC₄H⁺, MgC₆H⁺, and MgC₅N⁺ are consistent with observations, with differences no greater than one order of magnitude, corroborating radiative association as a plausible formation mechanism for these adducts. However, the calculated abundance of MgC₃N⁺ is about two orders of magnitude lower than observed, which indicates that either the chemistry of this species is significantly different from the others or the calculated rate coefficient is too low. The abundances obtained for Na-C₆H⁺ and Al-C₆H⁺ are around two orders of magnitude lower than for Mg, making very difficult to detect the analogous metal-bearing cations in IRC\,+10216.

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BibTeX RIS

BibTeX

@misc{bulut2026formation,
  title = {{Formation of adducts of C$_6$H with Na$^+$, Mg$^+$ and Al$^+$ metal cations by radiative association}},
  author = {Niyazi Bulut and Octavio Roncero and Maria Mallo and German Molpeceres and Marcelino Agundez and Maysa Yusef-Buey and Jose Cernicharo and Carlos Cabezas and Piotr Zuchowski},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.30126},
  eprint = {2609.30126},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.30126},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Formation of adducts of C_6H with Na^+, Mg^+ and Al^+ metal cations by radiative association
AU  - Niyazi Bulut
AU  - Octavio Roncero
AU  - Maria Mallo
AU  - German Molpeceres
AU  - Marcelino Agundez
AU  - Maysa Yusef-Buey
AU  - Jose Cernicharo
AU  - Carlos Cabezas
AU  - Piotr Zuchowski
PY  - 2026
DA  - 2026/09/25
PB  - arXiv
DO  - 10.48550/arxiv.2609.30126
UR  - https://arxiv.org/abs/2609.30126
AB  - The Mg-bearing cations MgC_4H^+, MgC_6H^+, MgC_3N^+, and MgC_5N^+ have been recently observed in the carbon-rich envelope IRC\,+10216. These species are thought to form upon radiative association between Mg^+ and the corresponding neutral radical. This work aims to determine the radiative association rate coefficients for the cations Al^+, Mg^+, and Na^+ reacting with carbon chain radicals to estimate the relative importance of metal-bearing carbon cations for each of these metals. For this purpose we use statistical methods in combination with highly accurate ab initio calculations to obtain the radiative association rate coefficient. Moreover, anisotropic effects beyond mono-dimensional capture model are considered, providing a more reliable description of the simulated processes.} The radiative association rate coefficients to form Mg-, Al- and Na-C_6H^+, as well as MgC_4H^+, MgC_3N^+, and MgC_5N^+, are calculated with the new restrictions considered in this work. These new rate coefficients are included in a chemical model of the C-rich AGB envelope IRC\,+10216. The abundances of MgC_4H^+, MgC_6H^+, and MgC_5N^+ are consistent with observations, with differences no greater than one order of magnitude, corroborating radiative association as a plausible formation mechanism for these adducts. However, the calculated abundance of MgC_3N^+ is about two orders of magnitude lower than observed, which indicates that either the chemistry of this species is significantly different from the others or the calculated rate coefficient is too low. The abundances obtained for Na-C_6H^+ and Al-C_6H^+ are around two orders of magnitude lower than for Mg, making very difficult to detect the analogous metal-bearing cations in IRC\,+10216.
ER  -

Formation of adducts of C₆H with Na⁺, Mg⁺ and Al⁺ metal cations by radiative association

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