Importance of surface morphology in interstellar H2 formation

Area of Science:

• Astrochemistry
• Solid-state physics
• Interstellar medium science

Background:

• Molecular hydrogen (H2) and its isotopologues are crucial in the interstellar medium (ISM).
• Understanding molecule formation on dust grains is key to astrochemistry.
• Previous studies focused on surface chemistry for H2 formation.

Purpose of the Study:

• Investigate the efficiency of HD formation from atom recombination on amorphous solid water (ASW).
• Determine the role of temperature and film morphology in HD formation.
• Analyze the energy release during H2 formation on dust grain analogs.

Main Methods:

• Laboratory experiments simulating interstellar conditions.
• Utilizing amorphous solid water films as dust grain analogs.
• Conducting atom recombination experiments in the temperature range of 8-20 Kelvin.

Main Results:

• HD formation via atom recombination on ASW films is highly efficient between 8-20 K.
• The fate of the 4.5 eV recombination energy strongly depends on the ASW film morphology.
• Efficient HD formation occurs at temperatures relevant for the ISM.

Conclusions:

• Grain morphology is more critical than surface chemistry for H2 formation energy release.
• This finding impacts models of molecule formation and energy balance in the ISM.
• Amorphous solid water films serve as relevant analogs for dust grains in the ISM.