A NEW CHEMICAL-MODEL OF THE CIRCUMSTELLAR ENVELOPE SURROUNDING IRC+10216

A new chemical model of the circumstellar envelope surrounding the car bon-rich star IRC+10216 has been developed. This model incorporates a variety of newly measured rapid neutral-neutral reactions between carb on atoms and hydrocarbons and between the radical CN and a variety of stable neutral molecules. In addition, other neutral-neutral reactions in the above two classes or involving atoms such as N or radicals suc h as C(2n)H have been included with large rate coefficients although t hey have not yet been studied in the laboratory. Unlike the interstell ar case, where the inclusion of these neutral-neutral reactions destro ys molecular complexity, our model results for IRC+10216 show that suf ficient abundances of large hydrocarbon radicals and cyanpolyynes can be produced to explain observations. We also discuss the formation of H2CN and NH2CN, two potentially observable molecules in IRC+10216.