Clocking Surface Reaction by In-Plane Product Rotation.

Area of Science:

• Surface science
• Physical chemistry
• Materials science

Background:

• Understanding electron-induced reactions on surfaces is crucial for molecular electronics and surface chemistry.
• Physisorbed molecules on metal surfaces offer unique reaction pathways influenced by substrate interactions.

Purpose of the Study:

• To investigate the electron-induced reaction mechanisms of meta-diiodobenzene (mDIB) on a Cu(110) surface at low temperatures.
• To differentiate between successive and concerted reaction pathways and their resulting product distributions.
• To utilize molecular dynamics to explain the observed differences in reaction outcomes.

Main Methods:

• Scanning Tunneling Microscopy (STM) was used to image molecular structures and reaction products.
• Molecular dynamics simulations were employed to model reaction pathways and dynamics.
• Experiments were conducted at cryogenic temperatures (4.6 K) to control molecular motion.

Main Results:

• Two distinct reaction mechanisms, successive and concerted, were identified for mDIB dissociation.
• The successive mechanism involved sequential C-I bond breaking, allowing iodophenyl intermediate rotation.
• The concerted mechanism involved simultaneous C-I bond breaking, with products reflecting unrotated mDIB.
• Molecular dynamics confirmed that the time delay between bond-breaking events dictates the extent of intermediate rotation.

Conclusions:

• The rotational dynamics of the iodophenyl intermediate act as a 'clock' for reaction timing.
• The difference in product distributions arises from the time available for intermediate rotation between bond-breaking events.
• This study presents a novel method to "clock" sub-picosecond dynamics by analyzing reaction product distributions.