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Contemporary galactic star formation occurs predominantly withingravitationally unstable, cold, dense molecular gas within supersonic,turbulent, magnetized giant molecular clouds (GMCs). Significantly, because thechemical evolution timescale and the turbulent eddy-turnover timescale arecomparable at typical GMC conditions, molecules evolve via inherentlynon-equilibrium chemistry which is strongly coupled to the dynamical evolutionof the cloud.  Current numerical simulation techniques, which include at most three decadesin length scale, can just begin to bridge the divide between the globaldynamical time of supersonic turbulent GMCs, and the thermal and chemicalevolution within the thin post-shock cooling layers of their backgroundturbulence. We address this GMC astrochemical scales problem using a solutionmethodology, which permits both complex three-dimensional turbulent dynamics aswell as accurate treatment of non-equilibrium post-shock thermodynamics andchemistry.  We present the current methodology in the context of the larger scope ofphysical processes important in understanding the chemical evolution of GMCs,including gas-phase chemistry, dust grains and surface chemistry, and turbulentheating. We present results of a new Lagrangian verification test forsupersonic turbulence. We characterize the evolution of these species accordingto the dimensionless local post-shock Damk\"{o}hler number, which quantifiesthe ratio of the dynamical time in the post-shock cooling flow to the chemicalreaction time of a given species.  Lastly, we discuss implications of this work to the selection of GMCmolecular tracers, and the zeroing of chemical clocks of GMC cores.

monthly notices of the royal astronomical society

The Astrochemical Evolution of Turbulent Giant Molecular Clouds : I -  Physical Processes and Method of Solution for Hydrodynamic, Embedded Starless  Clouds