Role of NH3 Binding Energy in the Early Evolution of Protostellar Cores

TL;DR

This study investigates how variations in ammonia's binding energy influence its abundance and the chemistry of protostellar cores, emphasizing the importance of multi-binding energy models for accurate astrochemical predictions.

Contribution

It introduces a systematic analysis of NH$_{3}$ binding energy effects on molecular abundances in protostellar cores using a gas-grain chemical network.

Findings

NH$_{3}$ abundance profiles are highly sensitive to binding energy values.

Higher binding energies result in lower gas-phase NH$_{3}$ abundances.

Binding energy variations significantly impact the formation of HNC, HCN, and CN.

Abstract

NH$_{3}$(ammonia) plays a critical role in the chemistry of star and planet formation, yet uncertainties in its binding energy (BE) values complicate accurate estimates of its abundances. Recent research suggests a multi-binding energy approach, challenging the previous single-value notion. In this work, we use different values of NH$_{3}$ binding energy to examine its effects on the NH$_{3}$ abundances and, consequently, in the early evolution of protostellar cores. Using a gas-grain chemical network, we systematically vary the values of NH$_{3}$ binding energies in a model Class 0 protostellar core and study the effects of these binding energies on the NH$_{3}$ abundances. Our simulations indicate that abundance profiles of NH$_{3}$ are highly sensitive to the binding energy used, particularly in the warmer inner regions of the core. Higher binding energies lead to lower gas-phase NH$_{3}$ abundances, while lower values of binding energy have the opposite effect. Furthermore, this BE-dependent abundance variation of NH$_{3}$ significantly affects the formation pathways and abundances of key species such as HNC, HCN, and CN. Our tests also reveal that the size variation of the emitting region due to binding energy becomes discernible only with beam sizes of 10 arcsec or less. These findings underscore the importance of considering a range of binding energies in astrochemical models and highlight the need for higher resolution observations to better understand the subtleties of molecular cloud chemistry and star formation processes.