What Molecular Abundances Can Tell Us About The Dynamics Of Star Formation

Molecular clouds are the sites where new stars form. Spectroscopic observations of different molecular species in these clouds can provide invaluable information regarding the dynamical evolution of star forming sites: first, they provide direct dynamical information (velocities as a function of density); second, they reveal the abundance of various molecules, which in turn depends on the chemodynamical evolutionary stage and history of the observed region. However, the connection between theoretical models of cloud dynamics and astronomical molecular spectroscopy is far from straight forward. The chemistry and dynamics of the clouds are interlinked, and various parameters such as the cloud temperature and its initial elemental abundances affect theoretical predictions, resulting in large model degeneracies: radically different dynamical models can often result in similar molecular abundances. In this talk, I will discuss first results from a massive effort undertaken to overcome this problem. By coupling non-equilibrium chemistry with a large array of different dynamical models of molecular cloud evolution, we are looking for these molecular line observables that are least affected by varying parameters and model degeneracies, and can be used to drastically constrain the possible dynamical histories of observed star-forming regions. To this end, we have studied a variety of dynamical models describing the evolution of pre- stellar molecular cloud cores (the initial phase of star formation) that cover the entire spectrum of proposed mechanisms, including pure hydrodynamical collACSe and magnetically mediated collACSe at various levels of importance of the magnetic field in the cloud dynamics. These models have been coupled to a network of chemical reactions that follow the relative abundances for $\sim$100 molecular species, by solving the non- equilibrium chemical reactions for the first time simultaneously with the dynamical equations. I will present highlights from the results of this work, including newly proposed observables with maximal potential for discrimination between different models of cloud evolution and star formation. These results are especially timely as ALMA is able to measure many of these quantities and contribute to the resolution of long-standing questions in star formation, such as the timescale of pre-stellar core evolution, and the relative importance of magnetic field and turbulence in their dynamics