Interaction of methanol with amorphous solid water.

Area of Science:

• Astrochemistry
• Surface Science
• Physical Chemistry

Background:

• Amorphous solid water (ASW) is a prevalent form of ice in interstellar environments.
• Understanding molecule-ice interactions is crucial for astrochemical models.
• Methanol (MeOH) is a key molecule in interstellar ice chemistry.

Purpose of the Study:

• To investigate the adsorption and interaction of methanol (MeOH) with amorphous solid water (ASW) ice.
• To determine the preferred orientation and binding sites of MeOH on ASW.
• To explore the co-deposition and interaction dynamics between MeOH and D2O.

Main Methods:

• Metastable-impact-electron spectroscopy
• Reflection-absorption infrared spectroscopy
• Temperature-programmed desorption mass spectroscopy
• Classical molecular dynamics (MD) simulations

Main Results:

• Methanol (MeOH) adsorbs with its hydroxyl group oriented towards dangling bonds of the ASW surface, forming strong hydrogen bonds.
• MD simulations at 190 K show MeOH forms a top layer on ASW, with MeOH-MeOH interactions becoming significant at higher coverages.
• Experimental results indicate D2O molecules embed into solid methanol films during co-deposition.

Conclusions:

• The adsorption of methanol on ASW is primarily governed by hydrogen bonding, dictating molecular orientation and layer growth.
• Intermolecular interactions between methanol molecules become important as the methanol layer thickens.
• The observed embedding of D2O into methanol films suggests complex co-deposition dynamics relevant to interstellar ice formation.