Opened 7 years ago

Last modified 3 years ago

#199 new enhancement

update to UMIST numerical fits to chemistry rates

Reported by: Gary J. Ferland Owned by: nobody
Priority: good to do Milestone: database infrastructure
Component: atomic/molecular data base Version: trunk
Keywords: UMIST update Cc:

Description Rollig -

Refit to numerically problematic UMIST reaction rate coefficients

  1. Röllig

(Submitted on 28 Mar 2011)

Aims. Chemical databases such as the UMIST Database for Astrochemistry (UDFA) are indispensable in the numerical modeling of astrochemical networks. Several of the listed reactions in the UDFA have properties that are problematic in numerical computations: Some are parametrized in a way that leads to extremely divergent behavior for low kinetic temperatures. Other reactions possess multiple entries that are each valid in a different temperature regime, but have no smooth transition when switching from one to another. Numerically, this introduces many difficulties.We present corrected parametrizations for these sets of reactions in the UDFA06 database. Methods. From the tabulated parametrization in UDFA, we created artificial data points and used a Levenberg-Marquardt algorithm to find a set of improved fit parameters without divergent behavior for low temperatures. For reactions with multiple entries in the database that each possess a different temperature regime, we present one joint parametrization that is designed to be valid over the whole cumulative temperature range of all individual reactions. Results. We show that it is possible to parametrize numerically problematic reactions from UDFA in a form that avoids low temperature divergence. Additionally, we demonstrate that it is possible to give a collective parametrization for reaction rate coefficients of reactions with multiple entries in UDFA. We present these new fitted values in tabulated form.

Comments: accepted by A&A Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Chemical Physics (physics.chem-ph) Cite as: arXiv:1103.5354v1 [astro-ph.IM]

Change History (1)

comment:1 Changed 3 years ago by Gary J. Ferland

Milestone: C13 branchdatabase infrastructure
Priority: majorgood to do

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