Understudied Classes of Ion-Molecule Reactions

Although most of the ion-molecule reactions used in large chemical models of interstellar clouds have not been studied in the laboratory, a few classes of reactions 

A second major class of ion-molecule reactions that is relatively poorly studied consists of systems involving very unsaturated hydrocarbon neutrals, especially radicals. The unsaturated nature of the organic chemistry in interstellar clouds leads to sizeable abundances of very unsaturated hydrocarbons such as the polyacetylenes HC H, the carbenes H2C , the radicals C H, and the clusters Cn. Although some work has been done on the chemistry of such species, much of the relevant ion-molecule chemistry involving ions such as C+, CH3, and even C2H2 must be guessed at from generalizations based on a small number of studied systems. 

Finally, the amount of laboratory information available to modelers seems to become more sparse as the reactants become larger. An extension of current models to include species with more than 10 atoms (as discussed below) is rendered highly speculative by the lack of experimental information. Particularly crucial are reactions leading to the formation and destruction of species in the same classes as observed molecules but somewhat larger in size. 

---