Abstract
Contemporary Galactic star formation occurs predominantly within gravitationally unstable, cold, dense molecular gas within supersonic, turbulent, magnetized giant molecular clouds (GMCs). Significantly, because the chemical evolution time-scale and the turbulent eddy-turnover time-scale are comparable at typicalGMCconditions, molecules evolve via inherently non-equilibrium chemistry which is strongly coupled to the dynamical evolution of the cloud. Current numerical simulation techniques, which include at most three decades in length-scale, can just begin to bridge the divide between the global dynamical time of supersonic turbulent GMCs, and the thermal and chemical evolution within the thin post-shock cooling layers of their background turbulence. We address this GMC astrochemical scales problem using a solution methodology, which permits both complex three-dimensional turbulent dynamics as well as accurate treatment of non-equilibrium post-shock thermodynamics and chemistry. We present the current methodology in the context of the larger scope of physical processes important in understanding the chemical evolution of GMCs, including gas-phase chemistry, dust grains and surface chemistry, and turbulent heating. We present results of a new-Lagrangian verification test for supersonic turbulence. We characterize the evolution of these species according to the dimensionless local post-shock Damkohler number, which quantifies the ratio of the dynamical time in the post-shock cooling flow to the chemical reaction time of a given species. Lastly, we discuss implications of this work to the selection of GMC molecular tracers, and the zeroing of chemical clocks of GMC cores.