Dr. Herbst and his team continue their investigations of astrochemistry in different environments of the interstellar medium, ranging from chemistry in molecular clouds to stellar outflows from AGB stars to the formation of prebiotic molecules, and some types of extragalactic sources. The focus is on improved chemical simulations of regions that will be observed in detail by ALMA and other interferometers to study both the dynamics and heterogeneity of sources. The work is done with chemical network computations which include gas-phase reactions and gas-surface (ice) reactions, as well as kinetic considerations. Observations of molecular spectra of the interstellar medium can be analyzed to tell us about the physical conditions of the objects in which the molecules reside. In order to understand how molecules are formed and destroyed, the PI and his team have created large networks for chemical reactions which include both gas-phase and grain-surface processes. Coupled with physical models of sources, either homogeneous or heterogeneous, these chemical network computations are used to calculate molecular abundances both in the gas and on the surfaces of dust grains. A comparison with observational data then gives us information on physical conditions and lifetimes of sources. Postdoc and graduate student training is a vital part of this project. The work in astrochemistry by the PI has been important in the burgeoning use of molecules as probes of the interstellar medium in our galaxy and others. Much of the knowledge of diffuse and dense interstellar clouds now comes from an understanding of what molecules in these regions tell us. The field of molecular astronomy has become a worldwide endeavor in which observational astronomers, theoretical chemists, experimental scientists, and modelers collaborate on problems of mutual interest.
