A spectral survey of IRC+10216 has been carried out in the range 11 to 14 \mu m with a spectral resolution of about 4 km s ^ { -1 } .
We have identified a forest of lines in six bands of C _ { 2 } H _ { 2 } involving the vibrational states from the ground to 3 \nu _ { 5 } and in two bands of HCN , involving the vibrational states from the ground up to 2 \nu _ { 2 } .
Some of these transitions are observed also in H ^ { 13 } CCH and H ^ { 13 } CN .
We have estimated the kinetic , vibrational , and rotational temperatures , and the abundances and column densities of C _ { 2 } H _ { 2 } and HCN between 1 and 300 R _ { * } ( \simeq 1.5 \times 10 ^ { 16 } cm ) by fitting about 300 of these ro-vibrational lines .
The envelope can be divided into three regions with approximate boundaries at 0 \arcsec \kern - 4.0 pt { . } \kern 1.0 pt 019 ( the stellar photosphere ) , 0 \arcsec \kern - 4.0 pt { . } \kern 1.0 pt 1 ( the inner dust formation zone ) , and 0 \arcsec \kern - 4.0 pt { . } \kern 1.0 pt 4 ( outer dust formation zone ) .
Most of the lines might require a large microturbulence broadening .
The derived abundances of C _ { 2 } H _ { 2 } and HCN increase by factors of 10 and 4 , respectively , from the innermost envelope outwards .
The derived column densities for both C _ { 2 } H _ { 2 } and HCN are \simeq 1.6 \times 10 ^ { 19 } cm ^ { -2 } .
Vibrational states up to 3000 K above ground are populated , suggesting pumping by near-infrared radiation from the star and innermost envelope .
Low rotational levels can be considered under LTE while those with J > 20 - 30 are not thermalized .
A few lines require special analysis to deal with effects like overlap with lines of other molecules .