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A spectral survey of IRC+10216 has been carried out in the range 11 to 14 umwith a spectral resolution of about 4 km s^-1. We have identified a forest oflines in six bands of C2H2 involving the vibrational states from the ground to3nu5 and in two bands of HCN, involving the vibrational states from the groundup to 2nu2. Some of these transitions are observed also in H13CCH and H13CN. Wehave estimated the kinetic, vibrational, and rotational temperatures, and theabundances and column densities of C2H2 and HCN between 1 and 300 R* (1.5E16cm) by fitting about 300 of these ro-vibrational lines. The envelope can bedivided into three regions with approximate boundaries at 0.019 arcsec (thestellar photosphere), 0.1 arcsec (the inner dust formation zone), and 0.4arcsec (outer dust formation zone). Most of the lines might require a largemicroturbulence broadening. The derived abundances of C2H2 and HCN increase byfactors of 10 and 4, respectively, from the innermost envelope outwards. Thederived column densities for both C2H2 and HCN are 1.6E19 cm^-2. Vibrationalstates up to 3000 K above ground are populated, suggesting pumping bynear-infrared radiation from the star and innermost envelope. Low rotationallevels can be considered under LTE while those with J>20-30 are notthermalized. A few lines require special analysis to deal with effects likeoverlap with lines of other molecules.

A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN