Published online by Cambridge University Press: 10 December 2009
Introduction
Giant interstellar clouds are the most massive chemical ‘factories’ in our Galaxy containing around 80 molecules presently identified (neglecting isotopic variants) and ranging in complexity from H2 and CO to large saturated molecules such as ethanol, CH3CH2OH, and highly unsaturated cyanopolyynes including the 13-atom chain HC11N. Millimetre and sub-millimetre observations of interstellar molecules allow one to probe the densities, temperatures, and dynamics of interstellar clouds and can give information on the initial conditions for star formation. It is also of interest to understand the chemistry of these molecules since chemical kinetic modelling can be used together with observational data to constrain uncertain parameters such as elemental abundances and the cosmic ray ionisation rate. An understanding of deuterium fractionation in interstellar molecules can be used to determine the D/H ratio and thus has a bearing on cosmological models of the origin of the universe.
In recent years models of increasing chemical, physical, and computational complexity have been developed to study molecular formation and destruction in various astronomical regions. Models of interstellar cloud chemistry can be divided roughly into two classes: (1) steady-state models, in which chemical abundances are calculated through solving a coupled system of non-linear algebraic equations; and (2) time-dependent models, in which the variations of abundances as a function of time are followed through solving a coupled system of stiff, non-linear, first-order, ordinary differential equations. Traditionally, steady-state models have been the dominant tool for studying chemistry in diffuse clouds which, in the absence of shocks, reach steady-state well within their lifetimes.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.