The magnesium paradigm in IRC+10216: Discovery of MgC\(_4\)H\(^+\), MgC\(_3\)N\(^+\), MgC\(_6\)H\(^+\), and MgC\(_5\)N\(^+\)

We found four series of harmonically related lines in IRC\,+10216 with the Yebes\,40m and IRAM\,30m telescopes. The first series corresponds to a molecule with a rotational constant, \(B\), of 1448.5994\(\pm\)0.0013 MHz and a distortion constant, \(D\), of 63.45\(\pm\)1.15 Hz and covers upper quantum numbers from \(J_u\)=11 up to 33 (B1449). The second series is fitted with \(B\)=1446.9380\(\pm\)0.0098 MHz and \(D\)=91\(\pm\)23 Hz and covers upper quantum numbers from \(J_u\)=11 up to 17 (B1447). The third series is fitted with \(B\)=598.7495\(\pm\)0.0011 MHz and D=6.13\(\pm\)0.43 Hz and covers quantum numbers from \(J_u\)=26 up to 41 (B599). Finally, the frequencies of the last series of lines can be reproduced with \(B\)=594.3176\(\pm\)0.0026 MHz and \(D\)=4.92\(\pm\)1.16 Hz (B594). The large values of \(D\) point toward four metal-bearing carriers. After exploring all plausible candidates containing Na, Al, Mg, and other metals, our ab initio calculations indicate that the cations MgC\(_4\)H\(^+\), MgC\(_3\)N\(^+\), MgC\(_6\)H\(^+\), and MgC\(_5\)N\(^+\) must be the carriers of B1449, B1447, B599, and B594, respectively. These cations could be formed by the radiative association of Mg\(^+\) with C\(_4\)H, C\(_3\)N, C\(_6\)H, and C\(_5\)N, respectively. We calculated the radiative association rate coefficient of Mg\(^+\) with C\(_4\)H, C\(_3\)N, C\(_6\)H, and C\(_5\)N and incorporated them in our chemical model. The results confirm that the Mg-bearing cations can be formed through these radiative association reactions in the outer layers of IRC\,+10216. This is the first time that cationic metal-bearing species have been found in space. These results provide a new paradigm on the reactivity of ionized metals with abundant radicals and open the door for further characterization of similar species in metal-rich astrophysical environments.