Laboratory Studies of Interstellar Dust Analogues for Astrochemical Modeling: Challenges and Future Directions for Understanding Chemical Evolution in Star-Forming Regions

Abstract

Astrochemical models are crucial for explaining molecular abundances across diverse astrophysical environments, ranging from the diffuse interstellar medium to planet-forming protoplanetary disks. However, their success depends on the accurate measurement of key physical parameters, such as the sticking of gaseous species to dust-grain or ice surfaces; desorption energies (Ed), which indicate how strongly adsorbed species bind to these surfaces; diffusion barriers (Eb), which control surface migration; and activation barriers that determine whether two adsorbed reactants can react upon encounter. In this review, we examine the current state of laboratory constraints on these parameters, together with the modeling approaches employed in contemporary astrochemical studies. Since interstellar grains are heterogeneous, laboratory studies use suitable analogues to approximate their surface composition and morphology. Experiments show that measured parameters vary widely with the surface morphology, coverage, ice composition, and experimental conditions. This makes it difficult to incorporate these parameters into astrochemical models that simulate the chemical evolution of astrophysical environments, leading to their underutilization in models. Standard simplifications such as fixed sticking coefficients, constant Eb/Ed ratios, and single-valued Eb and Ed values can propagate nonlinearly into model predictions. Finally, we discuss future laboratory requirements, including regime-dependent parametrization, independent measurements of diffusion barriers, and experiments on astrophysically relevant surfaces and ice compositions, together with modeling approaches that account for parameter distributions, environment-dependent surface properties, and hybrid stochastic-rate treatments. These developments would provide a more consistent link between microscopic surface processes and the observable chemical evolution.