The impact of rates of reactions with cosmic ray induced photons on chemical composition of protoplanetary discs

TL;DR

This study investigates how increased reaction rates with cosmic ray induced photons, influenced by dust growth, affect chemical compositions in protoplanetary discs, revealing significant changes in ice mass fractions but minimal effects on ionization levels.

Contribution

It introduces a modified astrochemical model accounting for larger dust sizes and higher reaction rates specific to protoplanetary discs, highlighting their impact on chemical abundances.

Findings

Increased reaction rates significantly alter ice mass fractions between 2 and 20 au.

Ionization degree remains largely unaffected by changes in reaction rates.

Dust growth influences the effectiveness of cosmic ray induced photon reactions.

Abstract

Cosmic rays and cosmic ray induced photons are vital components of chemical evolution in areas of interstellar medium that are impenetrable by external ultraviolet radiation. However, rates of reactions with cosmic ray induced photons used in astrochemical models were calculated for molecular clouds and can be different in protoplanetary discs, where dust grows up to larger sizes. Using ANDES astrochemical model, we study how an increase in both upper dust size and rates of reactions with cosmic ray induced photons can influence species abundances in protoplanetary discs. We show that the increase in these reactions' rates has a significant impact on the ice mass fraction in area between 2 and 20 au but has little impact on ionisation degree in disc.