Understanding H₂ Formation on Hydroxylated Pyroxene Nanoclusters: Ab Initio Study of the Reaction Energetics and...

Area of Science:

• Astrochemistry
• Computational Chemistry
• Materials Science

Background:

• Hydrogen molecule (H$_{2}$) formation is crucial for the interstellar medium (ISM).
• Silicate nanoclusters are potential catalysts for H$_{2}$ formation.
• The role of nanocluster hydroxylation in catalytic efficiency is not fully understood.

Purpose of the Study:

• To compute H$_{2}$ formation rate constants on silicate nanoclusters with varying hydroxylation.
• To evaluate the impact of hydroxylation on the catalytic efficiency of nanoclusters.
• To identify optimal nanocluster models for H$_{2}$ synthesis in the ISM.

Main Methods:

• Density functional methods and basis sets were tested for accuracy.
• Minimum energy reaction paths for H + H $\rightarrow$ H$_{2}$ were computed.
• Rate constants were calculated using semiclassical approaches (ZCT, SCT, SCTST).

Main Results:

• Hydroxylated nanoclusters (N=1-4) showed more efficient H$_{2}$ formation than bare ones.
• The (Mg$_{4}$Si$_{4}$O$_{12}$)(H$_{2}$O)$_{2}$ nanocluster exhibited the smallest reaction barrier and highest exothermicity.
• All studied nanoclusters proved efficient catalysts for H$_{2}$ formation in ISM conditions.

Conclusions:

• Hydroxylation significantly enhances the catalytic activity of silicate nanoclusters for H$_{2}$ formation.
• Moderately to highly hydroxylated pyroxene nanosilicates are superior catalysts compared to bare nanograins.
• These findings have implications for understanding chemical evolution in the ISM.