Context :

Aims : We model the chemistry of the inner wind of the carbon star IRC+10216 and consider the effects of periodic shocks induced by the stellar pulsation on the gas to follow the non-equilibrium chemistry in the shocked gas layers .
We consider a very complete set of chemical families , including hydrocarbons and aromatics , hydrides , halogens , and phosphorous-bearing species .
Our derived abundances are compared to those for the latest observational data from large surveys and the Herschel telescope .

Methods : A semi-analytical formalism based on parameterised fluid equations is used to describe the gas density , velocity , and temperature from 1 R _ { \star } to 5 R _ { \star } .
The chemistry is described using a chemical kinetic network of reactions and a set of stiff , ordinary , coupled differential equations is solved .

Results : The shocks induce an active non-equilibrium chemistry in the dust formation zone of IRC+10216 where the collision destruction of CO in the post-shock gas triggers the formation of O-bearing species such as H _ { 2 } O and SiO .
Most of the modelled molecular abundances agree very well with the latest values derived from Herschel data on IRC+10216 .
The hydrides form a family of abundant species that are expelled into the intermediate envelope .
In particular , HF traps all the atomic fluorine in the dust formation zone .
The halogens are also abundant and their chemistry is independent of the C/O ratio of the star .
Therefore , HCl and other Cl-bearing species should also be present in the inner wind of O-rich AGB or supergiant stars .
We identify a specific region ranging from 2.5 R _ { \star } to 4 R _ { \star } , where polycyclic aromatic hydrocarbons form and grow .
The estimated carbon dust-to-gas mass ratio derived from the mass of aromatics formed ranges from 1.2 \times 10 ^ { -3 } to 5.8 \times 10 ^ { -3 } and agrees well with existing values deduced from observations .
This aromatic formation region is situated outside hot layers where SiC _ { 2 } is produced as a bi-product of silicon carbide dust synthesis .
The MgS grains can form from the gas phase but in lower quantities than those necessary to reproduce the strength of the 30 \mu m emission band .
Finally , we predict that some molecular lines will show a flux variation with pulsation phase and time ( e.g. , H _ { 2 } O ) , while other species will not ( e.g. , CO ) .
These variations merely reflect the non-equilibrium chemistry that destroys and reforms molecules over a pulsation period in the shocked gas of the dust formation zone .

Conclusions :