Methods of Astrochemical Modeling: a Multidimensional Approach

Astrochemical kinetic models simulate the time-dependent chemical evolution of astrophysical environments by integrating a system of coupled, nonlinear differential rate law equations that describe the chemical reactions of a given molecular constituency. A general modeling method has been developed that varies the free parameters in the chemical model to generate grids of chemical structure that reveal for each species sensitivities to the model free parameters. Additionally, the general model takes as input functional representations of free parameters in the chemical kinetic model to generate a time-dependent chemical structure for systems of arbitrary geometry. Using a three-phase rate equation approach that includes species in the gas phase, on dust grains, and within ice mantles that develop on the grains, we model the chemical evolution for dark molecular cloud conditions observed in the Taurus Molecular Cloud 1 (TMC-1) and for the diffuse and translucent clouds observed toward Sagittarius B2 (Sgr B2). Several methods of fit are compared to determine the extent of the validity of agreement between observed and modeled relative molecular abundances using each method, and server tools have been developed to visualize and analyze the large datasets produced using our method in real time. Finally, the temperature-dependent reaction rate coefficients have been calculated for reactions involving sulfur and chlorine containing species likely to be present in the Venusian atmosphere, and the Arrhenius-Kooij parameters for a large temperature range T = 10 - 800 K have been optimized for integration into existing chemical networks.