Potential Paths for the Hydrogen-Bond Relaxing With (H₂O)_N Cluster Size.

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Unusual behavior in water nanodroplets and nanobubbles is linked to hydrogen bond (O:H-O) relaxation in undercoordinated molecules.
• Directly probing these intermolecular potentials has been a significant challenge.

Purpose of the Study:

• To develop a method for mapping the potential energy paths of O:H-O bonds in water clusters.
• To investigate how water cluster size influences hydrogen bond relaxation and associated properties.

Main Methods:

• Utilized the Lagrangian solution approach (Huang et al., 2013) to transform experimental bond lengths and phonon frequencies.
• Converted observed H-O bond (x = H) and O:H nonbond (x = L) lengths and phonon frequencies (dx, f077x) into force constants (kx) and bond energies (Ex).

Main Results:

• Molecular undercoordination reduces molecular size (dH) and enhances H-O bond energy (from 3.97 eV in bulk to 5.10 eV for a monomer).
• Undercoordination enlarges molecular separation (dL) and reduces O:H nonbond energy (from 95 meV to 35 meV for a dimer).
• Enhanced H-O energy raises melting point (273 K to 310 K), while reduced O:H energy lowers freezing temperature (258 K to 202 K for 1.4 nm droplets).

Conclusions:

• The developed method successfully maps potential energy paths for O:H-O bonds, correlating them with water cluster size.
• Changes in molecular undercoordination significantly impact water's energetic properties and phase transition temperatures.
• Findings provide insights into the fundamental interactions governing water's behavior at the nanoscale.