Effect of lowering gas-grain sticking coefficients on cold-core molecular abundances

¹ Aix Marseille Univ, CNRS, CINaM, Marseille, France
² Laboratoire d’Astrophysique de Bordeaux (LAB), Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
³ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir, km 4, Torrejón de Ardoz, 28850 Madrid, Spain

^⋆ Corresponding authors: caroline.stadler@univ-amu.fr; valentine.wakelam@u-bordeaux.fr; philippe.parent@univ-amu.fr

Received: 25 February 2025
Accepted: 19 June 2025

Abstract

Context. In dense environments, such as those found in cold cores, molecules from the gas phase stick at the surface of interstellar grains upon collision. Recent laboratory studies have shown that the adsorption probability of a gas-phase species on a grain, called the sticking coefficient (SC), is lower than the commonly used value of 1. This might significantly decrease the accretion rate of ice mantles onto the surface of grains and increase gas-phase abundances.

Aims. We used the Nautilus gas-grain numerical model to assess the effects of lower sticking coefficients on the evolution over time of molecular abundances in cold cores.

Methods. We compared the chemical abundances of gas-phase CO and CH₃OH between observations and model predictions, while using the sticking coefficients of 0.1, 0.3, and the standard value of 1 under cold-core conditions. Fixed and time-dependent physical conditions are assumed while the model results are compared to the observed abundances in the cold cores TMC-1, L694 and L429-C. This study combines rate equation chemical models with smoothed particle hydrodynamics (SPH) models.

Results. We find that lowering the sticking coefficient induces a temporal shift in the abundance profiles and can improve the agreement of the modeled abundances to observations. For CO, lower sticking coefficients also results in a strong decrease in the ice-to-gas ratio.

Conclusions. This work shows that it is possible to adjust the sticking coefficient toward more realistic values, and to obtain an agreement with the observed gas-phase abundances of the same quality, or even better, than with a SC of 1. However, a decrease in the SC causes the maxima of the calculated gas-phase abundances to be shifted in time.