Animated Movie of Ice

Jan 07, 2008

An animated movie shows an ordered structure dissolving little by little into a disordered mess after a light pulse: Swedish researchers from the University of Uppsala have used a computer to simulate ice melting after it is heated with a short light pulse.

As they report in the journal Angewandte Chemie, the absorbed energy first causes the OH bonds to oscillate. After a few picoseconds (10-12 s) the energy is converted into rotational and translational energy, which causes the crystal to melt, though crystalline domains remain visible for quite a while.

The common form of ice crystals is known as hexagonal ice. In this form the oxygen atoms of the water molecules are arranged in a tetrahedral lattice. Each water molecule is bound to four neighboring molecules by means of bridging hydrogen bonds, leading to an average of two bridges per molecule. In water, there are, on average, only 1.75 bridging hydrogen bonds per molecule.

What happens in the process of melting? Carl Caleman and David van der Spoel have now successfully used a computer to simulate “snapshots” of melting ice crystals. These molecular dynamics simulations are ideal for gaining a better understanding of processes like melting or freezing because they make it possible to simultaneously describe both the structure and the dynamics of a system with atomic resolution and with a time resolution in the femtosecond (10-15 s) range.

The simulation demonstrated that the energy of the laser pulse initially causes the OH bonds in the water molecules to vibrate. Immediately after the pulse, the vibrational energy reaches a maximum. After about a picosecond, most of the vibrational energy has been transformed into rotational energy.

The molecules begin to spin out of their positions within the crystal, breaking the bridging hydrogen bonds. After about 3 to 6 picoseconds, the rotations diminish in favor of translational motion. The molecules are now able to move freely and the crystal structure collapses. This process starts out locally, at individual locations within the crystal.

Once the symmetry of the structure is broken, the likelihood of melting processes occurring in the area immediately surrounding the crystal defect rises significantly. The melting process thus spreads out from this point little by little. At other locations the ice can maintain its crystalline structure a little longer.

A movie is available online at xray.bmc.uu.se/molbiophys/images/Movies/melt.mpg

Citation: David van der Spoel, Picosecond Melting of Ice by an Infrared Laser Pulse: A Simulation Study, Angewandte Chemie International Edition, doi: 10.1002/anie.200703987

Source: Angewandte Chemie

Explore further: Space-tested fluid flow concept advances infectious disease diagnoses

add to favorites email to friend print save as pdf

Related Stories

Scientists see urgent need for reducing emissions

Apr 15, 2014

(Phys.org) —The bad news: a major transformation of our current energy supply system is needed in order to avoid a dangerous increase in global temperatures. The good news: the technologies needed to get ...

Sustainable ways to keep us flying

Apr 09, 2014

The global aviation industry continues to expand, with over 3 billion people expected to fly commercially in 2014, along with 38 million metric tons of cargo. This activity will have a huge impact on the ...

Quantum melting

Apr 07, 2014

When ice is warmed, the water molecules forming its structure vibrate more and more vigorously until finally the forces between them are no longer strong enough to hold them together – the ice melts and ...

River ice reveals new twist on Arctic melt

Apr 02, 2014

A new study led by Lance Lesack, a Simon Fraser University geographer and Faculty of Environment professor, has discovered unexpected climate-driven changes in the mighty Mackenzie River's ice breakup. This ...

Recommended for you

User comments : 0

More news stories

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...

Impact glass stores biodata for millions of years

(Phys.org) —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...