Published online by Cambridge University Press: 14 August 2015
A discussion is given of the general processes and considerations that arise in attempting to understand molecular reactions in cool, dense interstellar clouds. Basic elements of the gas phase, “ion-molecule” scheme are given explicitly before surveying topics in which there is considerable current activity. These topics include: (i) refined comparisons of prediction and observation for species of “intermediate” complexity, (ii) numerical computations of cloud models which include numerous chemical reactions and molecular species, (iii) formation of the complex molecules, (iv) isotope fractionation in interstellar molecules and (v) possible contributions from chemistry in shocks.