Interaction of D2 with H2O amorphous ice studied by temperature-programmed desorption experiments.

Area of Science:

• Astrochemistry
• Surface Science
• Condensed Matter Physics

Background:

• Understanding gas-surface interactions on interstellar ice analogs is vital for astrochemical models.
• Porous amorphous solid water (ASW) is a relevant analog for icy grain mantles in the interstellar medium.
• Molecular hydrogen (D2) is a key species in interstellar chemistry, and its interaction with ice surfaces influences reaction pathways.

Purpose of the Study:

• To investigate the gas-surface interaction of D2 with porous ASW films.
• To determine the binding energies and desorption kinetics of D2 on ASW.
• To develop a model describing D2 adsorption and desorption on porous ice surfaces.

Main Methods:

• Thin films of porous ASW were grown at 10 K via slow vapor deposition.
• Temperature-programmed desorption (TPD) experiments were conducted to study D2 desorption.
• Arrhenius plot analysis was used to determine D2 binding energies as a function of coverage.
• A desorption kinetics model assuming thermal equilibrium and Fermi-Dirac statistics was developed.

Main Results:

• D2 rapidly diffuses into the porous ASW network.
• D2 desorption occurs between 10 and 30 K, probing the effective ASW surface.
• Asymmetric and broad distributions of D2 binding energies were observed, peaking at low energies.
• TPD curves were successfully simulated using a model based on a distribution of adsorption sites.

Conclusions:

• The study provides a detailed characterization of D2 binding energies on porous ASW.
• The developed model accurately describes D2 desorption kinetics, considering site heterogeneity.
• This work contributes to a better understanding of molecular hydrogen interactions with interstellar grain mantles.