Vibrational Förster transfer to hydrated protons

Area of Science:

• Physical Chemistry
• Spectroscopy
• Materials Science

Background:

• Vibrational energy relaxation is crucial for understanding molecular dynamics in liquids.
• The influence of excess protons on water's vibrational properties is not fully understood.
• O-H and O-D stretching modes in water are key to its unique properties.

Purpose of the Study:

• To investigate the effect of excess protons on vibrational energy relaxation in water.
• To elucidate the mechanism of energy transfer involving O-H and O-D stretching modes.
• To quantify the efficiency and distance dependence of proton-mediated energy transfer.

Main Methods:

• Femtosecond pump-probe spectroscopy was employed to study vibrational dynamics.
• Measurements were conducted on water samples with varying proton concentrations.
• Analysis focused on the decay kinetics of O-D stretch vibrations.

Main Results:

• Non-protonated water showed exponential O-D stretch decay (1.7 ps bulk, 4.3 ps anion-bound).
• Excess protons introduced a nonexponential decay pathway for O-D vibrations.
• This pathway was identified as distance-dependent dipole-dipole (Forster) interaction with dissolved protons.

Conclusions:

• Hydrated protons act as highly efficient vibrational energy acceptors in water.
• Forster energy transfer occurs over an average distance of 4.5 Å at 1M proton concentration.
• Proton-water interactions significantly alter vibrational energy relaxation dynamics.