SIMBAD references

We have updated the chemical model of IRC+10216 developed by Millar, Herbst & Bettens to include recent routes to the formation of sulphuretted hydrocarbons. The routes are based on a quantum chemical study of the S+C₂H system. In addition, we have altered the parent species for sulphur to reflect new observational results. We find that the model calculations give excellent agreement with the observed column densities, and discuss the significance of these reactions to the formation of species as yet unobserved and to dark interstellar clouds.