Temperature-programmed desorption of SO₂ from water ice surfaces: Adsorption energy distributions

¹ Sorbonne Université, CNRS, De la Molécule aux Nano-Objets: Réactivité, Interactions et Spectroscopies, MONARIS, 75005 Paris, France
² now at IRAP, Université de Toulouse, CNRS, UT3, CNES, Toulouse, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 9 March 2026
Accepted: 30 April 2026

Abstract

Context. Sulphur-bearing species play a key role in the chemical evolution of the interstellar medium and icy Solar System bodies such as the Jovian moons, yet the sulphur budget remains poorly constrained. Sulphur dioxide is considered one of the main sulphur reservoirs in icy environments, making its interaction with water ice surfaces highly relevant for astrochemical models.

Aims. This work aims to extract adsorption energy distributions of SO₂ on water ice substrates as a relevant model for astrophysical environments to better constrain its thermal behaviour and solid-gas exchange for astrochemical simulations.

Methods. We performed a systematic experimental study of temperature-programmed desorption of SO₂ deposited on three types of surfaces – polycrystalline gold, compact amorphous solid water (c-ASW), and crystalline water under ultra-high vacuum conditions – to then extract, using a Polanyi-Wigner model, the adsorption energy distributions of SO₂ on each surface.

Results. We performed the extraction of the adsorption energy distribution of SO₂ deposited on water ice substrates. These exhibit a bimodal structure: a first physisorbed layer and a second, more strongly bound population. Only minor differences are observed between c-ASW and crystalline water ice in the behaviour of the distributions. We also provide mean values, most probable values, and width of the distribution. On average, the binding energy of SO₂ on water ice surface is 439 ± 41 meV.