Quantum Tunneling Creates A Never Before Seen Shape For Water Molecules

New state of water: Strange 6-sided molecule found

 

A strange new behavior of water molecules has been observed inside crystals of beryl, a type of emerald, caused by bizarre quantum-mechanical effects that let the water molecules face six different directions at the same time.

Under normal conditions, the two hydrogen atoms in each water molecule are arranged around the oxygen atom in an open "V" shape, sometimes compared to a boomerang or Mickey Mouse ears.

But in a new experiment, scientists have found that hydrogen atoms of some water molecules trapped in the crystal structure of the mineral beryl become "smeared out" into a six-sided ring. 

The ring shape is caused by the "quantum tunneling" of the molecules, a phenomenon that lets subatomic particles pass or "tunnel" through seemingly-impossible physical barriers.

In this scenario, the atoms of the water molecule are "delocalized" among six possible directions inside natural hexagonal pores or channels that run though the crystal structure of the beryl, so it partially exist in all six positions at the same time, the researchers said.

Inside crystals 

Scientists from Oak Ridge National Laboratory (ORNL) in Tennessee and the Rutherford Appleton Laboratory in the United Kingdom observed the newly discovered effect in blue aquamarine crystals purchased at a gem show. Blue aquamarine; green and red emerald; pink morganite; gold heliodor; and clear goshenite gemstones are all varieties of the mineral beryl (beryllium aluminum cyclosilicate) with traces of other chemicals that give the crystals their characteristic colors.

"We chose beryl because it has a crystal structure that has channels in it, about 5 angstroms [5 ten-millionths of a millimeter] across — a little bit bigger than a water molecule — and it's known from spectroscopic data that natural beryls have water in them," said Larry Anovitz, a geochemist at ORNL and one of the authors of a paper on the new research. "We already know from lots of other studies that as you put water in smaller and smaller pores it starts to affect the properties of the water — the freezing point drops, the density changes, all sorts of things. So, we wanted to know, if you made that pore so small that you only can get a single molecule of water into it, what would that would do to the properties of water?"

What happened next was unexpected, Anovitz told Live Science.

"We knew that natural beryl would have water in these channels in the structure, so we could go and look at that and see what the properties were," he said. "But we didn't know that the properties would turn out to be so strange when we looked." 

Seeing a new state 

At ORNL's Spallation Neutron Source facility, after cooling the beryl crystals to very low temperatures, the scientists measured the lowest-energy states of the atoms in the trapped water molecules with neutron-scattering experiments, which use a beam of subatomic neutron particles to chart the motion of atoms and molecules.

"When we started looking at peaks in the inelastic neutron spectrum for this sample, we saw a number of peaks in the spectrum that, instead of getting bigger with temperature — which is what is expected to happen — they got smaller with temperature," Anovitz said.

"There are two ways this could happen — either by quantum tunneling or magnetic transitions — and we were able to prove that this is actually the quantum tunneling of the water molecules," he said.

Interactions between water molecules and the walls of the hexagonal channels usually force the water into the center of the channel, with both hydrogen "mouse ears" facing the same one of the six sides.

In their lowest energy states, the water molecules do not have enough energy to rotate to one of the adjacent positions.

But in the areas where the channels narrow so just a single water molecule can fit, the atoms in the water molecule can "tunnel" through the energy barrier that prevents rotation. And the new experiments reveal that the molecules were forming a "double-top" shape, with the proton nucleus of each hydrogen atom delocalizing into a six-sided ring around the central oxygen atom, the researchers said.

Measuring the molecules 

Alexander Kolesnikov, a physicist at ORNL and the lead author of the new paper, said additional studies at the Rutherford Appleton Laboratory had determined that the kinetic energy of the hydrogen protons in the six-sided water molecules was about 30 percent lower than in molecules of water in its normal state, or "bulk water."

"That is a direct indication that this is a quantum property due to the tunneling of water in this beryl channel," Kolesnikov told Live Science. "In classical terms, the kinetic energy would be expected to be something comparable to all other bulk water.

"This is not a new phase of water [like ice or steam] — it's not completely in the gas phase, but it's close to a gas phase," he added. "But at low temperatures, due to quantum delocalization, the kinetic energy of the protons significantly decreases, and they propagate under this [energy] barrier. So, I would say this is kind of a new state of the water molecule."

Anovitz said that quantum tunneling was known to occur in other substances but that the effect was usually limited to subatomic particles rather than larger particles like water molecules.

Quantum tunneling was also known to take place among hydrogen atoms in methyl-group molecules, which are arranged in a triangular pyramid shape around a carbon atom, but the molecules looked the same shape after the tunneling transition, he said.

"With water, when it's moving around this six-fold axis in the beryl channel, it doesn't look the same anymore — and that's something that's never been seen before," Anovitz said. 

Reference:

The findings were published April 22 in the journal Physical Review Letters.

Quantum Tunneling of Water in Beryl: A New State of the Water

Phys. Rev. Lett. 116, 167802

ONRL

The structural memory of water persists on a picosecond timescale

Long-lived sub-structures exist in liquid water as discovered using novel ultrafast vibrational spectroscopies.

Mainz/Amsterdam. A team of scientists from the Max Planck Institute for Polymer Research (MPI-P) in Mainz, Germany and FOM Institute AMOLF in the Netherlands have characterized the local structural dynamics of liquid water, i.e. how quickly water molecules change their binding state.

Using innovative ultrafast vibrational spectroscopies, the researchers show why liquid water is so unique compared to other molecular liquids. This study has recently been published in the scientific journal Nature Communications.

With the help of a novel combination of ultrafast laser experiments, the scientists found that local structures persist in water for longer than a picosecond, a picosecond (ps) being one thousandth of one billionth of a second (10-12 s). This observation changes the general perception of water as a solvent. “71% of the earth’s surface is covered with water. As most chemical and biological reactions on earth occur in water or at the air water interface in oceans or in clouds, the details of how water behaves at the molecular level are crucial. Our results show that water cannot be treated as a continuum, but that specific local structures exist and are likely very important” says Mischa Bonn, director at the MPI-P.

Water is a very special liquid with extremely fast dynamics. Water molecules wiggle and jiggle on sub-picosecond timescales, which make them undistinguishable on this timescale. While the existence of very short-lived local structures - e.g. two water molecules that are very close to one another, or are very far apart from each other - is known to occur, it was commonly believed that they lose the memory of their local structure within less than 0.1 picoseconds.

The proof for relatively long-lived local structures in liquid water was obtained by measuring the vibrations of the Oxygen-Hydrogen (O-H) bonds in water. For this purpose the team of scientists used ultrafast infrared spectroscopy, particularly focusing on water molecules that are weakly (or strongly) hydrogen-bonded to their neighboring water molecules. The scientists found that the vibrations live much longer (up to about 1 ps) for water molecules with a large separation, than for those that are very close (down to 0.2 ps). In other words, the weakly bound water molecules remain weakly bound for a remarkably long time.

Max Planck Institute for Polymer Research

Nanotechnology World Association

Filming the film: Scientists observe photographic exposure live at the nanoscale

Advanced method opens up new opportunities for investigation of dynamic processes

Photoinduced chemical reactions are responsible for many fundamental processes and technologies, from energy conversion in nature to micro fabrication by photo-lithography. One process that is known from everyday’s life and can be observed by the naked eye, is the exposure of photographic film. At DESY's X-ray light source PETRA III, scientists have now monitored the chemical processes during a photographic exposure at the level of individual nanoscale grains in real-time. The advanced experimental method enables the investigation of a broad variety of chemical and physical processes in materials with millisecond temporal resolution, ranging from phase transitions to crystal growth. The research team lead by Prof. Jianwei (John) Miao from the University of California in Los Angeles (UCLA) and Prof. Tim Salditt from the University of Göttingen report their technique and observations in the journal Nature Materials.

The researchers investigated a photographic paper (Kodak linagraph paper Type 2167or “yellow burn paper”) that is often used to determine the position of the beam at X-ray experiments. “The photographic paper we looked at is not specially designed for X-rays. It works by changing its colour on exposure to light or X-rays,” explains DESY physicist Dr. Michael Sprung, head of the PETRA III beamline P10 where the experiments took place.

The X-rays were not only used to expose the photographic paper, but also to analyse changes of its inner composition at the same time. The paper carries a photosensitive film of a few micrometre thickness, consisting of tiny silver bromide grains dispersed in a gelatine matrix, and with an average size of about 700 nanometres. A nanometre is a millionth of a millimetre. When X-rays impinge onto such a crystalline grain, they are diffracted in a characteristic way, forming a unique pattern on the detector that reveals properties like crystal lattice spacing, chemical composition and orientation. “We could observe individual silver bromide grains within the ‘burn’ paper since the X-ray beam had a size of only 270 by 370 nanometres – smaller than the average grain,” says Salditt, who is a partner of DESY in the construction and operation of the GINIX (Göttingen Instrument for Nano-Imaging with X-Rays) at beamline P10.

The X-ray exposure starts the photolysis from silver bromide to produce silver. An absorbed X-ray photon can create many photolytic silver atoms, which grow and agglomerate at the surface and inside the silver bromide grain. The scientists observed how the silver bromide grains were strained, began to turn in the gelatine matrix and broke up into smaller crystallites as well as the growth of pure silver nano grains. The exceptionally bright beam of PETRA III together with a high-speed detector enabled the ‘filming’ of the process with up to five milliseconds temporal resolution. “We observed, for the first time, grain rotation and lattice deformation during photoinduced chemical reactions,” emphasises Miao. “We were actually surprised how fast some of these single grains rotate,” adds Sprung. “Some spin almost one time every two seconds.”

“As advanced synchrotron light sources are currently under rapid development in the US, Europe and Asia,” the authors anticipate that “in situ X-ray nanodiffraction, which enables to measure atomic resolution diffraction patterns with several millisecond temporal resolution, can be broadly applied to investigate phase transitions, chemical reactions, crystal growth, grain boundary dynamics, lattice expansion, and contraction in materials science, nanoscience, physics, and chemistry.”

Reference:
Grain rotation and lattice deformation during photoinduced chemical reactions revealed by in situ X-ray nanodiffraction; Zhifeng Huang, Matthias Bartels, Rui Xu, Markus Osterhoff, Sebastian Kalbfleisch, Michael Sprung, Akihiro Suzuki, Yukio Takahashi, Thomas N. Blanton, Tim Salditt und Jianwei Miao; Nature Materials, 2015; DOI: 10.1038/NMAT4311

Source: http://www.desy.de/news/news_search/index_eng.html?openDirectAnchor=814