Theoretical Studies of Interstellar Matter

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Dr. Dalgarno will continue research on the chemical processes in the interstellar medium. Quantum mechanical calculations will be carried out on a variety of atomic and molecular processes that are significant in astrophysical environments with particular attention to processes occurring in the interstellar medium and in the ejecta of supernova 1987A. Theoretical studies will be performed on the ionization structure, heating and cooling mechanisms and the molecular composition of supernovae, interstellar clouds, and the influence of ultraviolet photons and X-rays on the structure of molecular clouds in galaxies. The infrared response of molecular hydrogen to X-rays will be calculated. Although it is extremely tenuous, the interstellar medium (ISM) is the site of many complicated atomic and molecular reactions. Essentially all elements are present in varying quantities, and they are known to combine to form diverse molecules such as water, ammonia, alcohol, and even more complicated species. Also, larger particles of ice and dust are present. This complicated medium is then continually bombarded with various sources of energy including cosmic rays, X-rays, low and high energy photons, collisions between atoms and molecules, shock waves, various bulk movements of the ISM, and turbulent kinetic energy. This reactive "soup" quite expectedly emits photons from many electronic transitions and observing these gives data on the physical and chemical conditions in the vast space between the stars. However, because of the complications involved, interpretation of ISM observations is not straightforward and requires laboratory measurements and quantum mechanical calculations for their understanding. Dr. Dalgarno's highly regarded theoretical research is directed toward furthering our understanding of the constituents and activity in the ISM.