Chemists Form World's Smallest Droplet Of Acid

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ScienceDaily (June 22, 2009) — Exactly four water molecules and one hydrogen chloride molecule are necessary to form the smallest droplet of acid. This was the result of work by the groups of Prof. Dr. Martina Havenith (physical chemistry) and Prof. Dr. Dominik Marx (theoretical chemistry) within the research group FOR 618. They have carried out experiments at ultracold temperatures close to absolute zero temperature using infrared laser spectroscopy to monitor the molecules.

This has been accompanied by theoretical ab initio simulations. According to their calculations, the reaction at these extremely cold temperatures is only possible if the molecules are aggregating one after the other.
Chemistry at ultracold temperatures in space
If you put a classical acid, for example hydrogen chloride in water, the acid molecules will preferentially lose a proton (H+). Thereby the pH-value of the solution is decreased and the solution becomes acidic. In particular, so-called hydronium ions (H3O+), are formed by protonated water molecules. This hydronium ion is an important ingredient in many chemical reactions. Despite of the fact that this is one of the most fundamental reactions, it was not clear until now how many water molecules are actually required in order to form a charge separated negative Cl- ion and a positive H3O+ ion. “Whereas we all know acids from our daily life, we have now been able to observe for the first time acid formation on a molecular level.” "We will need this knowledge in order to understant chemical processes on nanoscopic structures, on small particles and on surfaces” explains Prof. Havenith-Newen. This indicates that there is a rich chemistry even at very low temperatures; a fundamental basis for reactions within stratospheric clouds or in interstellar media. Previously, it had been unclear whether reactions with only a few water molecules can take place at theses ultracold temperatures.
Ultracold trap
For their experiments, the researchers have successively embedded hydrogen chloride as well as single water molecules in a special ultracold trap. They used nanodroplets of suprafluid helium which have a temperature of less than -272,8 °C. Molecules will first be cooled down before they have a chance to aggregate. “Suprafluid” is a special property of the helium which implies that the embedded molecules are still free to rotate before they are frozen, thereby allowing monitoring with unsurpassed precision. Captured in such a way, it is possible to obtain the chemical fingerprint of the acid – its infrared spectrum. By combining trapping with high resolution IR laser spectroscopy and theoretical calculations, the chemists demonstrated that exactly four water molecules are required to form the smallest droplet of acid: (H3O)+(H2O)3Cl-.
Important: One molecule after the other
After these results, the researchers were left with the question of how this reaction can take place at ultracold temperatures near absolute zero. “Usually, activation of chemical reactions requires the input of energy, just like for cooking at home you need a cooking plate or a gas flame” explains Prof. Marx. “However, how should this be possible at a few Kelvin (close to absolute zero)?” The calculations, in combination with experiment, showed that the reaction is only possible by a successive aggregation process. Instead of putting together 4 water molecules and an HCl molecule simultanesously at the beginning and the waiting for a dissociation process to occur, they found in their simulations that when adding the water molecules step by step, a proton is transferred exactly when adding the fourth water molecule. Then, a hydronium ion will immediately form with one of the four added water molecules. This unusual mechanism is called “aggregation induced dissociation”. “We suspect that such aggregation induced reactions, can explain chemical transformations at ultracold conditions, such as can be found at small ice particles in clouds and in interstellar media”, explains Prof. Marx.
The work which described here is part of the research unit FOR 618 “Understanding the Aggregation of Small Molecules with Precise Methods - Interplay between Experiment and Theory”( Co-ordinator: Prof. Dr. Wolfram Sander (Faculty of Chemistry and Biochemistry) which has been funded by the Germany Science Foundation and which has just been extended for three more years after successful evaluation.
Journal reference:
Anna Gutberlet, et al. Below 1 K: The Smallest Droplet of Acid Aggregation-Induced Dissociation of HCl(H2O)4. Science, 324, 1545 (2009) DOI: 10.1126/science.1171753
Adapted from materials provided by Ruhr-Universitaet-Bochum, via AlphaGalileo.

The Laser Glow of an Atom Cloud

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Random lasers are the "disco ball" version of normal lasers. Instead of beaming in one direction, the light is scattered out in all directions by particles in a powder, for example. Calculations described in the 1 May Physical Review Letters show that a cloud of cold atoms could form a new type of random laser, where individual atoms scatter and amplify the light. The work suggests that the atoms will begin lasing if the cloud can be made opaque, or "cloudy," enough, which the authors think is within reach of current technology. Because such a system is fundamentally simple, it may give insight into some of the mysteries of random lasers.
A normal laser is essentially a gain medium inside a reflective cavity. The light is amplified by the medium as it bounces back and forth between the cavity's mirrors. A random laser has no cavity. Instead, tiny "mirrors," or scatterers, are added to the gain medium, causing photons to bounce around and become amplified by the medium, before escaping in all directions. For example, a container of micron-sized particles floating in water in which a laser dye has also been dissolved can emit laser light if pumped with external light. Random lasers do not require the same precise manufacturing as normal lasers, so they could be inexpensive to produce. Potential applications include digital displays, light emitting paints, and temperature sensors.
There are, however, some uncertainties regarding the spectra and time variability of random lasers [see Focus story: "Photon Marathon"]. So Robin Kaiser of Nice Sophia Antipolis University and the National Center for Scientific Research (CNRS) in France and his colleagues considered a random laser made up of cold atoms. Such a system would not have the absorption and other difficult-to-model complexities of existing random lasers. However, "it was not clear that atoms would be able to play the roles of both gain medium and scatterers," says Nice team member William Guerin. A single atom scatters photons when it's in its ground state and amplifies photons (through stimulated emission) when it's in an excited state, but it can't do both at the same time. So the researchers needed to find the right balance of atoms in both ground and excited states.
The team modeled a two-level atomic system. In their scenario, a complicated three-photon transition--made possible by an external pump laser--keeps a sufficient fraction of the atoms in the excited state (a so-called population inversion) from which they can provide gain. For different pump frequencies and intensities, the researchers calculated the amount of scattering necessary to trap light in the cloud long enough for it to become true "coherent" laser light, with all the photons propagating in synch. They quantified the amount of scattering within the cloud with a number called the optical thickness [1]. A value between 200 and 250 would lead to lasing, they found, which is within reach of state-of-the-art cold atom traps that currently achieve 150, Guerin says.
The researchers performed a simulation showing that the laser light should be detectable over background light coming from the cloud. They are now trying to make such a random laser in the lab using a standard magneto-optical trap to hold the atoms. Guerin says there are tricks to compress the trap to increase the density and therefore the amount of scattering.
There may, however, be experimental challenges involving the non-uniform density of the cloud, says Diederik Wiersma of the European Laboratory for Non-linear Spectroscopy in Florence, Italy. But if it can work, the use of atoms, rather than micron-scale scatterers, "could enrich our understanding of the random laser phenomena," Wiersma says. Moreover, because cold atoms are capable of slowing down light, he speculates that they could be more efficient at trapping light than current techniques. --Michael Schirber Michael Schirber is a freelance science writer in Lyon, France.
References:[1] The optical thickness--a characterization of the "opaqueness" of the atoms--can be thought of as the diameter of the cloud measured in units of the "mean free path," which is the typical distance a photon travels before scattering. This refers to scattering with the pump laser turned off, when there is no lasing.
Related Information:Related info:
Focus story: Photon Marathon (2004)
more explanation of random lasers from Wiersma's lab web site
Threshold of a Random Laser with Cold Atoms Luis S. Froufe-Pérez, William Guerin, Rémi Carminati, and Robin Kaiser Phys. Rev. Lett. 102, 173903 (issue of 1 May 2009)

Quantum Mechanics Predicts Unusual Lattice Dynamics Of Vanadium Metal Under Pressure

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http://www.sciencedaily.com/releases/2007/10/071011125338.htm

Science Daily — A Swedish research team of Dr. Wei Luo & Professor Rajeev Ahuja and US team of Dr. Y. Ding & Prof. H.K. Mao have used theoretical calculations to understand a totally new type of high-pressure structural phase transition in Vanadium. This phase was not found in earlier experiments for any element and compound. These findings are being published in the Proceedings of the National Academy of Science.
The relation between electronic structure and the crystallographic atomic arrangement is one of the fundamental questions in physics, geophysics and chemistry. Since the discovery of the atomic nature of matter and its periodic structure, this has remained as one of the main questions regarding the very foundation of solid systems.
Scientists at Carnegie's Geophysical Laboratory, USA and Uppsala University, Sweden have discovered a new type of phase transition - a change from one form to another-in vanadium, a metal that is commonly added to steel to make it harder and more durable. Under extremely high pressures, pure vanadium crystals change their shape but do not take up less space as a result, unlike most other elements that undergo phase transitions. This work was appeared in the February 23, 2007 issue of Physical Review Letters.
Trying to understand why high-pressure vanadium uniquely has the record-high superconducting temperature of all known elements inspired us to study high-pressure structure of vanadium. Usually high superconductivity is directly linked to the lattice dynamics of material.
In present paper in PNAS, again a collaboration between Uppsala University and Carnegie's Geophysical Laboratory, USA, we have looked in to the lattice dynamics of vanadium metal and it shows a very unusual behavior under pressure.
A huge change in the electronic structure is driving force behind this unusual lattice dynamics. Moreover, our findings provide a new explanation for the continuous rising of superconducting temperature in high-pressure vanadium, and could lead us to the next breakthrough in superconducting materials.
Note: This story has been adapted from material provided by Uppsala University.

Fausto Intilla
www.oloscience.com

Taming Tiny, Unruly Waves For Nano Optics

Source:

http://www.sciencedaily.com/releases/2007/10/071008113705.htm

Science Daily — Nanoscale devices present a unique challenge to any optical technology — there’s just not enough room for light to travel in a straight line.

On the nanoscale, energy may be produced by radiating photons of light between two surfaces very close together (sometimes as close as 10 nanometers), smaller than the wavelength of the light. Light behaves much differently on the nanoscale as its wavelength is interrupted, producing unstable waves called evanescent waves. The direction of these unpredictable waves can’t be calculated, so researchers face the daunting task of designing nanotechnologies to work with the tiny, yet potentially useful waves of light.
Researchers at Georgia Tech have discovered a way to predict the behavior of these unruly waves of light during nanoscale radiation heat transfer, opening the door to the design of a spectrum of new nanodevices (or NEMS) and nanotechnologies, including solar thermal energy technologies.
“This discovery gives us the fundamental information to determine things like how far apart plates should be and what size they should be when designing a technology that uses nanoscale radiation heat transfer,” said Zhuomin Zhang, a lead researcher on the project and a professor in the Woodruff School of Mechanical Engineering. “Understanding the behavior of light at this scale is the key to designing technologies to take advantage of the unique capabilities of this phenomenon.”
The Georgia Tech research team set out to study evanescent waves in nanoscale radiation energy transfer (between two very close surfaces at different temperatures by means of thermal radiation). Because the direction of evanescent waves is seemingly unknowable (an imaginary value) in physics terms, Zhang’s group instead decided to follow the direction of the electromagnetic energy flow (also known as a Poynting vector) to predict behavior rather than the direction of the photons.
“We’re using classic electrodynamics to explain the behavior of the waves, not quantum mechanics,” Zhang said. “We’re predicting the energy propagation — and not the actual movement — of the photons.”
The challenge is that electrodynamics work differently on the nanoscale and the Georgia Tech team would need to pinpoint those differences. Planck’s law, a more than 100-year-old theory about how electromagnetic waves radiate, does not apply on the nanoscale due to fact that the space between surfaces is smaller than a wavelength.
The Georgia Tech team observed that instead of normal straight line radiation, the light was bending as protons tunneled through the vacuum in between the two surfaces just nanometers apart. The team also noticed that the evanescent waves were separating during this thermal process, allowing them to visualize and predict the energy path of the waves.
Understanding the behavior of such waves is critical to the design of many devices that use nanotechnology, including near-field thermophotovoltaic systems, nanoscale imaging based on thermal radiation scanning tunneling microscopy and scanning photon-tunneling microscopy, said Zhang.
These findings were featured on the cover of the Oct. 8 issue of Applied Physics Letters.
Note: This story has been adapted from material provided by Georgia Institute of Technology.

Fausto Intilla

www.oloscience.com

Laser Joining Of Solar Cells

Source:

http://www.sciencedaily.com/releases/2007/10/071007203636.htm

Science Daily — A single solar cell produces a relatively low output – it’s a case of strength in numbers. Tiny strips of metal are used to link cells together. If the laser soldering temperature is too high, the solder joint may fracture. A new system provides automatic temperature regulation.

Teamwork is what matters – even in the case of solar cells: To obtain sufficient power to operate a pocket calculator, parking ticket dispenser or photovoltaic module, sunlight has to be captured simultaneously by an array of cells. They are connected in series using tiny strips of metal known as stringers. Each stringer has to be positioned in precisely the right spot, then its solder coating is melted using a hot electrode.
When the solder sets, it forms a stable bond with the metallic coating on the silicon. The amount of heat induced in the stringer and the silicon depends on the contact between the soldering electrode and the stringer. Applying too much energy causes thermal stress which in the worst case could destroy the solder joint, leaving a break in the electrical circuit that makes the solar module unfit for use.
Researchers at the Fraunhofer Institute for Laser Technology ILT in Aachen have developed a non-contact soldering system in which the temperature is constantly monitored. If the temperature deviates beyond set limits, the system automatically adjusts it to an acceptable value. “Instead of an electrode, we use a laser beam for the soldering operation,” says ILT department head Dr. Arnold Gillner.
“To melt the solder, we pass a laser beam over the solder-coated stringer. An infrared heat camera derives the temperature of the silicon and of the metal strip from real-time measurements of their emitted radiant heat. If the temperature is too high or too low, a feedback control circuit automatically adapts the laser output within milliseconds.” The system is already in use for industrial surface engineering applications. Solar applications could be on the market in a year or so.
The researchers’ next project is to develop a faster, more reliable method of connecting solar cells by means of laser welding. “Whereas soldering only involves melting the solder, in laser welding the stringer itself is melted,” explains Gillner. This means applying more heat than for soldering, but only for a very short time. “Since the laser is only in contact with the materials for a brief instant, only a small amount of energy is transferred to the materials despite the higher temperature – resulting in even fewer heat-induced defects,” he adds.
What complicates the matter is the fact that the stringer has a diameter of about 200 micrometers, whereas the metallic coating on the silicon required to conduct electricity has a thickness of a mere 10 micrometers. The laser beam has to be modulated in such a way that the stringer will melt while leaving the coating on the silicon intact.
Note: This story has been adapted from material provided by Fraunhofer-Gesellschaft.

Fausto Intilla

www.oloscience.com

Sodium Loses Its Luster: A Liquid Metal That's Not Really Metallic

Source:

http://www.sciencedaily.com/releases/2007/09/070926155621.htm

Science Daily — When melting sodium at high pressures, the material goes through a transition in which its electrical conductivity drops threefold.

In a series of new calculations, Lawrence Livermore National Laboratory scientists describe the unusual melting behavior of dense sodium.
"We found that molten sodium undergoes a series of pressure-induced structural and electronic transitions similar to those observed in solid sodium but beginning at a much lower pressure," said LLNL's Eric Schwegler.
Schwegler and former colleagues Stanimir Bonev, now at Dalhousie University in Nova Scotia, and Jeans-Yves Raty at FNRS-University of Liège in Belgium report the new findings in the Sept. 27 edition of the journal, Nature.
Earlier experimental measurements of sodium's melting curve have shown an unprecedented pressure-induced drop in melting temperature from 1,000 K at 30 GPa (30,000 atmospheres of pressure) down to room temperature at 120 GPa (120 million atmospheres of pressure).
Usually when a solid melts, its volume increases. In addition, when pressure is increased, it becomes increasingly difficult to melt a material.
However, sodium tells a different story.
As pressure is increased, liquid sodium initially evolves into a more compact local structure. In addition, a transition takes place at about 65 GPa that is associated with a threefold drop in electrical conductivity.
The researchers carried out a series of first-principle molecular dynamic simulations between 5 and 120 GPa and up to 1,500 K to investigate the structural and electronic changes in compressed sodium that are responsible for the shape of its unusual melting curve.
The team discovered that in addition to a rearrangement of the sodium atoms in the liquid under pressure, the electrons were transformed as well. The electronic cloud gets modified; the electrons sometimes get trapped in interstitial voids of the liquid and the bonds between atoms adopt specific directions.
"This behavior is totally new in a liquid as we usually expect that metals get more compact with pressure," Raty said.
Note: This story has been adapted from material provided by DOE/Lawrence Livermore National Laboratory.

Fausto Intilla

www.oloscience.com

Official Kilogram Losing Mass: Scientists Propose Redefining It As A Precise Number Of Carbon Atoms

Source:

http://www.sciencedaily.com/releases/2007/09/070921110735.htm

Science Daily — How much is a kilogram?

It turns out that nobody can say for sure, at least not in a way that won't change ever so slightly over time. The official kilogram -- a cylinder cast 118 years ago from platinum and iridium and known as the International Prototype Kilogram or "Le Gran K" -- has been losing mass, about 50 micrograms at last check. The change is occurring despite careful storage at a facility near Paris.
That's not so good for a standard the world depends on to define mass.
Now, two U.S. professors -- a physicist and mathematician -- say it's time to define the kilogram in a new and more elegant way that will be the same today, tomorrow and 118 years from now. They've launched a campaign aimed at redefining the kilogram as the mass of a very large -- but precisely-specified -- number of carbon-12 atoms.
"Our standard would eliminate the need for a physical artifact to define what a kilogram is," said Ronald F. Fox, a Regents' Professor Emeritus in the School of Physics at the Georgia Institute of Technology. "We want something that is logically very simple to understand."
Their proposal is that the gram -- 1/1000th of a kilogram -- would henceforth be defined as the mass of exactly 18 x 14074481 (cubed) carbon-12 atoms.
The proposal, made by Fox and Theodore P. Hill -- a Professor Emeritus in the Georgia Tech School of Mathematics -- first assigns a specific value to Avogadro's constant. Proposed in the 1800s by Italian scientist Amedeo Avogadro, the constant represents the number of atoms or molecules in one mole of a pure material -- for instance, the number of carbon-12 atoms in 12 grams of the element. However, Avogadro's constant isn't a specific number; it's a range of values that can be determined experimentally, but not with enough precision to be a single number.
Spurred by Hill's half-serious question about whether Avogadro's constant was an even or odd number, in the fall of 2006 Fox and Hill submitted a paper to Physics Archives in which they proposed assigning a specific number to the constant -- one of about 10 possible values within the experimental range. The authors pointed out that a precise Avogadro's constant could also precisely redefine the measure of mass, the kilogram.
Their proposal drew attention from the editors of American Scientist, who asked for a longer article published in March 2007. The proposal has so far drawn five letters, including one from Paul J. Karol, chair of the Committee on Nomenclature, Terminology and Symbols of the American Chemical Society. Karol added his endorsement to the proposal and suggested making the number divisible by 12 -- which Fox and Hill did in an addendum by changing their number's final digit from 8 to 6. So the new proposal for Avogadro's constant became 84446886 (cubed), still within the range of accepted values.
Fast-forward to September 2007, when Fox read an Associated Press article on the CNN.com Web site about the mass disappearing from the International Prototype Kilogram. While the AP said the missing mass amounted to no more than "the weight of a fingerprint," Fox argues that the amount could be significant in a world that is measuring time in ultra-sub-nanoseconds and length in ultra-sub-nanometers.
So Fox and Hill fired off another article to Physics Archive, this one proposing to redefine the gram as 1/12th the mass of a mole of carbon 12 -- a mole long being defined as Avogrado's number of atoms. They now hope to generate more interest in their idea for what may turn out to be a competition of standards proposals leading up to a 2011 meeting of the International Committee for Weights and Measures.
At least two other proposals for redefining the kilogram are under discussion. They include replacing the platinum-iridium cylinder with a sphere of pure silicon atoms, and using a device known as the "watt balance" to define the kilogram using electromagnetic energy. Both would offer an improvement over the existing standard -- but not be as simple as what Fox and Hill have proposed, nor be exact, they say.
"Using a perfect numerical cube to define these constants yields the same level of significance -- eight or nine digits -- as in those integers that define the second and the speed of light," Hill said. "A purely mathematical definition of the kilogram is experimentally neutral -- researchers may then use any laboratory method they want to approximate exact masses."
The kilogram is the last major standard defined by a physical artifact rather than a fundamental physical property. In 1983, for instance, the distance represented by a meter was redefined by how far light travels in 1/299,792,458 seconds -- replacing a metal stick with two marks on it.
"We suspect that there will be some public debate about this issue," Fox said. "We want scientists and science teachers and others to think about this problem because we think they can have an impact. Public discussion may play an important role in determining how one of the world's basic physical constants is defined."
How important is this issue to the world's future technological development"
"When you make physical and chemical measurements, it's important to have as high a precision as possible, and these standards really define the limits of precision," Fox said. "The lack of an accurate standard leaves some inconsistency in how you state results. Having a unique standard could eliminate that."
While the new definition would do away with the need for a physical representation of mass, Fox says people who want a physical artifact could still have one -- though carbon can't actually form a perfect cube with the right number of atoms. And building one might take some time.
"You could imagine having a lump of matter that actually had exactly the right number of atoms in it," Fox noted. "If you could build it by some kind of self-assembly process -- as opposed to building it atom-by-atom, which would take a few billion years -- you could have new kilogram artifact made of carbon. But there's really no need for that. Even if you built a perfect kilogram, it would immediately be inaccurate as soon as a single atom was sloughed off or absorbed."
Note: This story has been adapted from a news release issued by Georgia Institute of Technology.

Fausto Intilla

www.oloscience.com

'Radio Wave Cooling' Offers New Twist On Laser Cooling

Source:

http://www.sciencedaily.com/releases/2007/09/070914105600.htm

Science Daily — Visible and ultraviolet laser light has been used for years to cool trapped atoms--and more recently larger objects--by reducing the extent of their thermal motion.

Now, applying a different form of radiation for a similar purpose, physicists at the National Institute of Standards and Technology (NIST) have used radio waves to dampen the motion of a miniature mechanical oscillator containing more than a quadrillion atoms, a cooling technique that may open a new window into the quantum world using smaller and simpler equipment.
Described in a forthcoming issue of Physical Review Letters,* this demonstration of radio-frequency (RF) cooling of a relatively large object may offer a new tool for exploring the elusive boundary where the familiar rules of the everyday, macroscale world give way to the bizarre quantum behavior seen in the smallest particles of matter and light. There may be technology applications as well: the RF circuit could be made small enough to be incorporated on a chip with tiny oscillators, a focus of intensive research for use in sensors to detect, for example, molecular forces.
The NIST experiments used an RF circuit to cool a 200 x 14 x 1,500 micrometer silicon cantilever--a tiny diving board affixed at one end to a chip and similar to the tuning forks used in quartz crystal watches--vibrating at 7,000 cycles per second, its natural "resonant" frequency. Scientists cooled it from room temperature (about 23 degrees C, or 73 degrees F) to -228 C (-379 F).
Other research groups have used optical techniques to chill micro-cantilevers to lower temperatures, but the RF technique may be more practical in some cases, because the equipment is smaller and easier to fabricate and integrate into cryogenic systems. By extending the RF method to higher frequencies at cryogenic temperatures, scientists hope eventually to cool a cantilever to its "ground state" near absolute zero (-273 C or -460 F) , where it would be essentially motionless and quantum behavior should emerge.
Laser cooling is akin to using the kinetic energy of millions of ping-pong balls (particles of light) striking a rolling bowling ball (such as an atom) to slow it down. The RF cooling technique, lead author Kenton Brown says, is more like pushing a child on a swing slightly out of synch with its back-and-forth motion to reduce its arc. In the NIST experiments, the cantilever's mechanical motion is reduced by the force created between two electrically charged plates, one of which is the cantilever, which store energy like electrical capacitors.
In the absence of any movement, the force would be stable, but in this case, it is modulated by the cantilever vibrations. The stored energy takes some time to change in response to the cantilever's movement, and this delay pushes the cantilever slightly out of synch, damping its motion.
* K.R. Brown, J. Britton, R.J. Epstein, J. Chiaverini, D. Leibfried, and D.J. Wineland. 2007. Passive cooling of a micromechanical oscillator with a resonant electric circuit. Physical Review Letters. [Forthcoming].
Note: This story has been adapted from a news release issued by National Institute of Standards and Technology.

Fausto Intilla

www.oloscience.com