Chemical model for dense portion of the nearby globule Barnard (B68)

We have studied the chemistry of the isolated globule Barnard (B68). The chemical evolution is studied using pseudo-time-dependent and contracting models, involving pure gas-phase and gas-grain chemistry. Our results confirm the importance of grain chemistry in predicting the observed species in B68. We have also outlined the impact of using contracting models on producing more reliable results of the chemical evolution of the dark clouds such as B68.