Ultrafast dynamics in Na-doped water clusters and the solvated electron

Area of Science:

• Physical Chemistry
• Chemical Physics
• Spectroscopy

Background:

• Investigating the excited-state dynamics of water-alkali metal clusters provides insights into electron-phonon coupling.
• Understanding energy relaxation pathways in nanoscale systems is crucial for various chemical and physical processes.

Purpose of the Study:

• To measure and analyze the excited-state lifetimes of sodium-doped water clusters ((H2O)n...Na and (D2O)n...Na).
• To elucidate the mechanisms of energy redistribution and relaxation in these clusters.

Main Methods:

• Utilizing two-color pump-probe spectroscopy with femtosecond laser pulses (800 and 400 nm).
• Measuring excited-state lifetimes for clusters with n up to 40.

Main Results:

• Excited-state lifetime decreases rapidly from 1.2 ps (n=2) to ~100 fs (n>=10).
• Deuterated clusters ((D2O)n...Na) show lifetimes approximately 3.6 times longer than their hydrogenated counterparts.
• Energy redistribution is attributed to the conversion of electronic excitation into ground-state vibrations.

Conclusions:

• A model based on Fermi's Golden Rule qualitatively predicts trends but not exact lifetimes.
• The energy gap law and the role of water stretching modes explain the longer lifetimes in deuterated clusters.
• Water stretching modes are significant in the energy transfer processes within these clusters.