Observations with the Yebes 40 m telescope toward IRC +10216. The left and right panels show the lines of B1449 and B1447 (MgC₄H⁺ and MgC₃N⁺), respectively. The line parameters are given in Tables A.1 and A.2, respectively. The abscissa corresponds to the rest frequency assuming a local standard of rest velocity of −26.5 km s⁻¹. The ordinate is the antenna temperature corrected for atmospheric and telescope losses in millikelvin. The red lines show the fitted line profiles adopting a terminal velocity of expansion of 14.5 km s⁻¹ (Cernicharo et al. 2000).