Various C12Clx+ ions (x = 0-10) are formed from electron impact on decachloroacenaphthene, C12Cl10. The structures of these ions are determined using ion chromatography. It is found that the graphitic carbon backbone persists down to C12Cl4+. Small amounts of monocyclic structures appear for C12Cl6+ and C12Cl4+ and are exclusive for C-12(+). The linear structure first appears at C12Cl4+ and is exclusive for C12Cl2+ and C12Cl+. For the most part, these results are consistent with predictions from semiempirical PM3 calculations, indicating thermochemistry plays a major role in determining isomer distributions. In several cases, other factors have to be considered, the most important being isomerization barriers and the effect of entropy. Doubly charged ions are observed for a significant number of cases. Graphitic structures disappear below C12Cl62+ and are replaced by monocyclic and linear isomers, again consistent with PM3 calculations.