Attachment cross sections of protonated water clusters

Area of Science:

• Physical Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• Understanding molecular interactions with water clusters is crucial for atmospheric and chemical processes.
• Previous studies have explored water cluster formation but lacked detailed collision dynamics.
• Protonated water clusters serve as fundamental models for studying solvation and proton transfer.

Purpose of the Study:

• To experimentally investigate the attachment dynamics of water molecules onto size-selected protonated water clusters.
• To measure absolute attachment cross sections across varying collision energies, cluster sizes, and temperatures.
• To elucidate the underlying mechanisms governing water molecule attachment, particularly at higher collision energies.

Main Methods:

• Size-selected protonated water clusters were prepared and subjected to collisions with water molecules.
• Absolute attachment cross sections were measured as a function of collision energy, cluster size, and temperature.
• Experimental data were analyzed to identify dynamical effects influencing attachment probability.

Main Results:

• Attachment cross sections were found to decrease significantly below hard sphere predictions as collision energy increased.
• This reduction was attributed to a transition from adiabatic to non-adiabatic collision regimes.
• Results with deuterated water clusters corroborated the proposed dynamical effect related to energy redistribution times.

Conclusions:

• Collision duration, rather than cluster temperature, dictates attachment probability at higher energies.
• A dynamical effect, where insufficient time exists for energy redistribution, limits attachment.
• The findings highlight the importance of vibrational mode periods in determining collision outcomes for water clusters.