Important ion-atom and ion-molecule collisions in astrophysics

As the early universe evolved, electrons, multiply-charged ions, singly-charged ions, atoms and sim le molecules formed, generating primordial gas clouds. These molecules are believed to have triggered protostar formation acting as precursors to galaxies. As material was processed in and ejected from stars the interstellar medium in galaxies adopted the diverse character that is now observed. The phases of coronal gas, HII regions, circumstellar shells, HI regions, diffuse ana molecular clouds, supernova remnants, shocked regions and comets are all evident. Within the phases of the interstellar medium, a wealth of gas-phase ion-atom and ion-molecule interactions generates species which modify the evolution of the phases. The predominant ton-neutral reaction processes in these media will be discussed, with emphasis on general trends in the reactivity and product identity.