PDF_CHEM: Fast simulations of the chemical ISM using probability distributions

We present PDF CHEM , a new numerical method able to compute the photodissociation region (PDR) chemistry of large-scale inhomogeneous ISM regions using probability distributions physical parameters as an input. distinguish between two visual extinctions, namely ‘effective’ ( A V,eff ) referring local extinction and ‘observed’ V,obs taken from observations. Using 1,200 pre-calculated PDR simulations, we apply hypothetical −PDFs, representing diffuse Giant Molecular Cloud. PDFchem is fast can replace computationally expensive hydrodynamical models in understanding different environments, including at low metallicities high cosmic-ray ionization rates.