Polycyclic Aromatic Hydrocarbons (PAHs) are one of the most common chemical compounds on Earth. These big molecules are naturally present in crude oil and coal deposits, and are also formed by... Show morePolycyclic Aromatic Hydrocarbons (PAHs) are one of the most common chemical compounds on Earth. These big molecules are naturally present in crude oil and coal deposits, and are also formed by incomplete combustion of carbon-containing fuels, hence they are found in car exhaust, cigarette smoke and (too) well-cooked meats. This makes PAHs one of the most widespread organic pollutants. In space, PAHs are an important and ubiquitous component of the Interstellar Medium, dominating the mid-infrared emission of many astronomical objects. However, very little is known about the destiny of PAHs when they are bombarded by high-velocity ions and electrons arising from interstellar shocks, hot gas and cosmic rays (CRs). The research described in this thesis shows that in shocks with velocities above 100 km/s and in a million-degree gas, PAHs are completely destroyed by collisions with electrons, and can survive only if isolated in denser clouds. Destruction by CRs is due to collisions with ions. Because of their high energy (5 MeV - 10 GeV) CRs can access these denser clouds and will set the lifetime of those protected PAHs, which can be used as a __dye__ for tracing the presence of material entrained in the hot gas. Show less