| We examine the role cosmic rays, X-rays and ultra-violet (UV) photons play in the chemical evolution of the interstellar medium, and how astrophysical processes like massive star formation can change the fluxes of these energetic particles. We connect star formation rates to interstellar chemistry.;We first explore the basic effects of cosmic-ray and X-ray ionization and UV photodissociation on the chemistry. For cosmic-ray and X-ray ionization, increasing the ionization rates enriches the chemistry, up to a value of 10 -14 s-1, whereupon molecules and ions are quickly destroyed due to the high electron fraction. Isolated from other effects, the UV field tends to dissociate species much more efficiently than ionizing them, and generally reduces molecular abundances, especially those of complex molecules. The combination of a high ionization rate and a high UV field can enhance the production of some molecular species, such as small hydrocarbons.;We investigate the role of cosmic rays and UV photons in the Horsehead Nebula, and determine the impact a column-dependent cosmic ray ionization rate makes on photodissociation region (PDR) chemistry. The column-dependence of cosmic rays is solved using a three-dimensional two-fluid magnetohydrodynamics model, treating the cosmic rays as a fluid governed by the relativistic Boltzmann Transport Equation, and treating the interstellar medium as a second fluid, governed by the standard non-relativistic magnetohydrodynamics equations.;We then utilize a modified version of the Morata-Herbst time-dependent PDR model, incorporating our function for cosmic ray ionization. Our results help solve a chemical mystery concerning high abundances of small hydrocarbons at the edge of the nebula. We discuss predictions the model makes for species currently unobserved in the Horsehead Nebula.;Finally, we examine the role of star formation on interstellar astrochemistry in the Orion KL region. We develop a new astrochemical gas-grain PDR model with a time-dependent UV radiation field and X-ray and cosmic ray flux, scaled to the star formation rate and radiative contributions of different spectral-type stars. The results provide an explanation for OH+, H2O + and water observations, and H3O+ non-detection in the region, as well as make unique predictions for HCO+ and other molecules. These results allow us to constrain the age of the Orion KL region. We predict an age for Orion KL of one hundred thousand to one million years after OB star formation. |
