We have detected the (0,11c,0)J=3-2 and (0,0,0)J=8-7 transitions of HCN towards the S star {chi} Cygni. The excitation requirements of these transitions are too high to be satisfied in the outer envelope of the star, and the emission must originate within {solar}20 stellar radii, ie. the molecule must be forming close to the star. This conclusion is supported by a model for AGB stars in which molecules including HCN form in a shocked wind close to the stellar surface.
@article{arxiv.astro-ph/0006188,
title = {HCN in the inner envelope of {chi} Cygni},
author = {Debiprosad Duari and Jennifer Hatchell},
journal= {arXiv preprint arXiv:astro-ph/0006188},
year = {2007}
}