Spontaneously polarised crystalline water ice

Area of Science:

• Solid-state physics
• Materials science
• Spectroscopy

Background:

• The conventional model of hexagonal ice (Ih) assumes random orientation of water molecular dipoles.
• This assumption has persisted for nearly a century in scientific literature.
• Understanding the precise structure of ice is crucial for various scientific disciplines.

Purpose of the Study:

• To investigate the molecular structure of hexagonal ice (Ih) using advanced spectroscopic techniques.
• To determine if hexagonal ice exhibits net molecular orientation.
• To challenge and potentially revise the existing structural model of ice Ih.

Main Methods:

• Utilizing vacuum-ultraviolet absorption spectroscopy to probe the ice structure.
• Preparing hexagonal ice (Ih) films via condensation of pure water vapor on an insulating substrate (MgF2).
• Analyzing Stark shifts in absorption spectra to detect molecular orientation and internal fields.

Main Results:

• Hexagonal ice (Ih) prepared from pure water vapor shows net molecular orientation.
• This orientation indicates ordered proton disposition, contradicting the random dipole model.
• Spontaneous polarization and internal electric fields of approximately 4 × 10^6 V m^-1 were observed in thin ice films.

Conclusions:

• The established model of hexagonal ice (Ih) requires revision due to observed molecular orientation.
• Proton order, not randomness, characterizes the structure of hexagonal ice.
• The findings reveal intrinsic electric fields within hexagonal ice, with implications for its physical properties.