Refit to numerically problematic UMIST reaction rate coefficients

TL;DR

This paper improves the numerical stability of reaction rate coefficients in the UMIST Database for Astrochemistry by providing corrected parametrizations that avoid divergence at low temperatures and unify multiple entries across temperature regimes.

Contribution

It introduces new parametrizations for problematic reactions in UDFA06, ensuring numerical stability and consistency across temperature ranges.

Findings

Corrected reaction rate parametrizations avoiding low-temperature divergence.

Unified multiple reaction entries into a single smooth parametrization.

Presented tabulated fitted values for practical use.

Abstract

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.