Ionization potentials of large sodium doped ammonia clusters

Area of Science:

• Physical Chemistry
• Atomic and Molecular Physics
• Condensed Matter Physics

Background:

• Ammonia clusters are model systems for studying solvation effects.
• Understanding the behavior of electrons in clusters is crucial for various chemical and physical processes.

Purpose of the Study:

• To investigate the ionization potentials (IP) of sodium-doped ammonia clusters, Na(NH3)n.
• To determine how IP changes with cluster size (n).
• To compare experimental results with theoretical models, specifically the dielectric continuum model.

Main Methods:

• Generation of Na(NH3)n clusters via supersonic expansion and sodium atom doping.
• Photoionization of clusters using a tunable dye laser system.
• Mass analysis of ions using a reflectron time-of-flight mass spectrometer to measure size-dependent ionization potentials.

Main Results:

• Observed a continuous decrease in ionization potential with increasing cluster size for n > 17.
• Identified a plateau for 10 ≤ n ≤ 17 and smaller steps at n = 24, 35, and 59.
• Extrapolated ionization potential for infinite cluster size (IP(n=infinity)) to be 1.66 ± 0.01 eV.
• IPs showed a linear relationship with (n+1)^(-1/3), consistent with the dielectric continuum model.

Conclusions:

• The observed size-dependent ionization potentials support the dielectric continuum model for solvated electrons in ammonia clusters.
• The extrapolated IP(n=infinity) provides a benchmark for bulk ammonia properties.
• Differences in IPs compared to negative ammonia cluster ions and liquid ammonia solutions are attributed to counterion effects and their distances from the solvated electron.