carbon chains in IRC+10216, it is only activated in a very specific region of the outer envelope. However, there are still many open questions such as whether all carbon chains occur precisely in the same circumstellar region or whether there is some degree of radial stratification depending on the carbon chain length. A deeper look into the exact chemical mechanisms behind the formation of carbon chains requires observations with a significantly higher sensitivity and angular resolution.

In this article, we present sensitive ALMA observations of IRC+10216 in several rotational lines of carbon chains across the $\lambda$ 3 mm band. The observations have an angular resolution of $\sim$1$''$, which allows us to resolve the detailed structure and to precisely locate the circumstellar regions where the emission of each carbon chain arises. A chemical model has been developed to interpret the observations and to explain the carbon chain chemistry that is taking place in the outer envelope of this archetypal carbon star.

Observations {#sec:observations}
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A $\lambda~3$ mm spectral survey of IRC+10216 covering the frequency range 84.0-115.5 GHz was carried out with ALMA band3 during Cycle2. Observations were obtained with compact and extended array configurations. The field of view (primary beam) of 