Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Weizmann Scientists Observe Quantum Effects in Cold Chemistry

15.10.2012
At very low temperatures, close to absolute zero, chemical reactions may proceed at a much higher rate than classical chemistry says they should – because in this extreme chill, quantum effects enter the picture.

A Weizmann Institute of Science team has now confirmed this experimentally; their results will not only provide insight into processes in the intriguing quantum world in which particles act as waves, but they might explain how chemical reactions occur in the vast frigid regions of interstellar space.

Long-standing predictions are that quantum effects should allow the formation of a transient bond – one that will force colliding atoms and molecules to orbit each other, instead of separating after the collision. Such a state would be very important, as orbiting atoms and molecules could have multiple chances to interact chemically. In this theory, a reaction that would seem to have a very low probability of occurring would proceed very rapidly at certain energies.

Dr. Ed Narevicius and his team in the Institute’s Department of Chemical Physics managed, for the first time, to experimentally confirm this elusive process in a reaction they performed at chilling temperatures of just a fraction of a degree above absolute zero – 0.01°K. Their results appeared this week in Science.

“The problem,” says Dr. Narevicius, “is that in classical chemistry, we think of reactions in terms of colliding billiard balls held together by springs on the molecular level. In the classical picture, reaction barriers block those billiard balls from approaching one another, whereas in the quantum physics world, reaction barriers can be penetrated by particles, as these acquire wave-like qualities at ultra-low temperatures.“

The quest to observe quantum effects in chemical reactions started over half a century ago with pioneering experiments by Dudley Herschbach and Yuan T. Lee, who later received a Nobel Prize for their work. They succeeded in observing chemical reactions at unprecedented resolution by colliding two low-temperature, supersonic beams. However, the collisions took place at relative speeds that were much too high to resolve many quantum effects: when two fast beams collide, the relative velocity sets the collision temperature at above 100°K, much too warm for quantum effects to play a significant role. Over the years, researchers have used various ingenious techniques, including changing the angle of the beams and slowing them down to a near-halt, that managed to bring the temperatures down to around 5°K – close, but still a miss for those seeking to observe chemical reactions in quantum conditions.

The innovation that Dr. Narevicius and his team, including Alon B. Henson, Sasha Gersten, Yuval Shagam, and Julia Narevicius, introduced was to merge the beams rather than collide them. One beam was produced in a straight line, and the second beam was bent using a magnetic device until it was parallel with the first. Even though the beams were racing at high speed, the relative speed of the particles in relation to the others was zero; thus, a much lower collision temperature of only 0.01K could be achieved. One beam contained helium atoms in an excited state; the other, either argon atoms or hydrogen molecules. In the ensuing chemical reaction, the argon or hydrogen molecules became ionized, releasing electrons.

To see if quantum phenomena were in play, the researchers looked at reaction rates – a measure of how fast a reaction proceeds – at different collision energies. At high collision energies, classical effects dominated and the reaction rates slowed down gradually as the temperature dropped. But below about 3°K, the reaction rate in the merged beams suddenly took on peaks and valleys. This is a sign that a quantum phenomenon – known as scattering resonances, due to tunneling – was occurring in the reactions. At low energies, particles started behaving as waves; those waves that were able to tunnel through the potential barrier interfered constructively with the reflected waves upon collision. This creates a standing wave that corresponds to particles trapped in orbits around one another. Such interference occurs at particular energies and is marked by a dramatic increase in reaction rates.

Says Dr. Narevicius: “Our experiment is the first proof that the reaction rate can change dramatically in the cold reaction regime. Beyond the surprising results, we have shown that such measurements can serve as an ultrasensitive probe for reaction dynamics. Our observations already prove that our understanding of even the simplest ionization reaction is far from complete; it requires a thorough rethinking and the construction of better theoretical models. We expect that our method will be used to solve many puzzles in reactions that are especially relevant to interstellar chemistry, which generally occurs at ultra-low temperatures.”

Dr. Edvardas Narevicius is the incumbent of the Ernst and Kaethe Ascher Career Development Chair.

The Weizmann Institute of Science in Rehovot, Israel, is one of the world's top-ranking multidisciplinary research institutions. Noted for its wide-ranging exploration of the natural and exact sciences, the Institute is home to 2,700 scientists, students, technicians, and supporting staff. Institute research efforts include the search for new ways of fighting disease and hunger, examining leading questions in mathematics and computer science, probing the physics of matter and the universe, creating novel materials, and developing new strategies for protecting the environment.

Jennifer Manning | Newswise Science News
Further information:
http://www.weizmann-usa.org

More articles from Physics and Astronomy:

nachricht Unraveling the nature of 'whistlers' from space in the lab
15.08.2018 | American Institute of Physics

nachricht Early opaque universe linked to galaxy scarcity
15.08.2018 | University of California - Riverside

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

Staying in Shape

16.08.2018 | Life Sciences

Diving robots find Antarctic seas exhale surprising amounts of carbon dioxide in winter

16.08.2018 | Earth Sciences

Protein droplets keep neurons at the ready and immune system in balance

16.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>