Probing methanol cluster growth by vacuum ultraviolet ionization

Area of Science:

• Physical Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• Understanding cluster formation and growth is crucial for solvation and nucleation phenomena.
• Mass spectrometry is a powerful tool for probing molecular cluster dynamics.

Purpose of the Study:

• To investigate the formation and growth dynamics of methanol clusters using mass spectrometry.
• To understand the factors influencing the abundance of protonated methanol clusters at different ionization distances.

Main Methods:

• Generating methanol clusters in a molecular beam.
• Ionizing clusters using vacuum ultraviolet (VUV) radiation at varying distances from the nozzle.
• Analyzing cluster distributions via time-of-flight mass spectrometry.
• Obtaining mass spectra and photoionization onsets for optimized cluster conditions.

Main Results:

• Cluster intensity distributions varied significantly with nozzle-to-ionization distance.
• Ion-molecule reactions dominated closer to the nozzle, favoring protonated species.
• The protonated trimer was most abundant at shorter distances due to solvation shell effects and photoionization cross-section.
• The protonated dimer became most abundant at farther distances due to low neutral density and enhanced monomer-neutral interactions.

Conclusions:

• The study elucidates the distinct formation pathways of protonated methanol clusters based on ionization proximity.
• Thomson's liquid drop model provides a qualitative framework for understanding the observed cluster distributions.
• These findings contribute to fundamental knowledge of solvation and nucleation processes.