Metallic water: Transient state under ultrafast electronic excitation

Area of Science:

• Condensed matter physics
• Materials science
• Physical chemistry

Background:

• Controlled irradiation with femtosecond lasers or swift heavy ion beams can achieve high energy densities.
• These conditions can lead to collective electronic excitation, reaching the warm dense matter state.
• In this state, particle interaction potential energy is comparable to kinetic energy (few eV).

Purpose of the Study:

• To investigate the response of bulk water to ultrafast electronic excitation.
• To understand the resulting changes in interatomic potentials and material properties.
• To identify the mechanisms driving ion acceleration and chemical transformations.

Main Methods:

• Density functional theory (DFT) calculations.
• Tight-binding molecular dynamics (TBMD) simulations.
• Studying bulk water under ultrafast electronic excitation.

Main Results:

• A threshold electronic temperature induces bandgap collapse, making water electronically conducting.
• High irradiation doses result in nonthermal ion acceleration to thousands of Kelvins within femtoseconds.
• The interplay between nonthermal mechanisms and electron-ion coupling enhances energy transfer.
• Disintegration of water molecules forms various chemically active fragments, dependent on the deposited dose.

Conclusions:

• Ultrafast electronic excitation fundamentally alters water's properties, inducing conductivity and nonthermal ion heating.
• These processes create unique nonequilibrium states of matter with altered chemistry.
• The findings provide insights into matter under extreme conditions and radiation-induced chemistry.