Featured Research

from universities, journals, and other organizations

Chemists find new dimension to rules for reactions

Date:
October 25, 2011
Source:
Emory University
Summary:
Theoretical chemists have solved an important mystery about the rates of chemical reactions and the so-called Polanyi rules. The findings reveal why a reaction involving methane does not conform to the known rules, a problem that has baffled physical chemists in recent years. Long-range, their findings could play a role in the development of cleaner, more efficient fuels.

Theoretical chemists at Emory University have solved an important mystery about the rates of chemical reactions and the so-called Polanyi rules.

Related Articles


The findings, published in the journal Science, reveal why a reaction involving methane does not conform to the known rules, a problem that has baffled physical chemists in recent years.

"We showed that a pre-reactive, long-range force can align the reaction of a chorine atom with methane, or natural gas, in a way that actually inhibits the reaction," says Joel Bowman, a professor of theoretical chemistry at Emory and the Cherry L. Emerson Center for Computational Chemistry. "We believe that the theoretical work that we did has extended and modified the Polanyi rules."

Bowman published the results with Gabor Czako, a post-doctoral fellow in theoretical chemistry who performed most of the complex computational and mathematical analyses that uncovered the results.

Long-range, their findings could play a role in the development of cleaner, more efficient fuels.

Understanding the dynamics of chemical reactions is key to driving reactions efficiently, whether in a laboratory experiment or in an industrial application. In 1986, John Polanyi shared the Nobel Prize in chemistry, in part by providing general rules for how different forms of energy affect the rates of reactions.

"The Polanyi rules tell you the best way to deposit energy in a simple molecule to make a chemical reaction occur," Bowman says. "It's a bit like knowing in advance how to invest $1,000 to maximize the return on investment."

Polanyi developed the framework based on studies of simple reactions of chlorine and fluorine atoms with hydrogen gas. As technology has advanced in recent years, some chemists began testing the Polanyi rules for more complicated reactions, and the rules appeared to break down. Most notably, sophisticated molecular beam experiments by Kopin Liu at the Institute of Atomic and Molecular Sciences in Taiwan showed that the reaction of halogen atoms with methane did not conform to the rules.

"Suddenly, the rules appeared to have changed, and no one could explain why," Bowman says. "We decided to roll up our sleeves and attack the problem theoretically."

Bowman and Czako drew from the computational power of the Emerson Center, specialized software and analytical techniques. They first created theoretical-computational simulations of the experiments done by Liu and others, and then described the results mathematically.

"Our calculations showed essentially an exact agreement with the experimental results," Bowman says. "When theory and experiment agree you're happy, but you still want to know why."

Determining why the reactions did not conform to the Polanyi rules was another complicated task, involving quantum mechanics and forces that govern the reaction down to the atomic level.

"As theoreticians, we're able to zoom in and look at the results of our calculations in a way that's virtually impossible in an experiment," Bowman says.

They identified a subtle interplay between the Polanyi rules and a pre-reactive long-range force of methane with chlorine. If you follow the Polanyi rules, this long-range force, or steric control, will misalign the reactants, preventing them from docking correctly and inhibiting a reaction. But if you apportion the energy in the opposite way to the rules, the misalignment is wiped out and the reaction occurs.

"This long-range force was playing a bigger role than was previously realized," Bowman says. "It can actually trump the Polanyi rules, at least in the reactions that Liu and we looked at. The Polanyi rules are certainly not all wrong, they just appear to be too simple to apply to more complex reactions."

The research was funded by the National Science Foundation and the U.S. Department of Energy.

The reactive properties of natural gas are of particular interest since it is an important fuel. Bowman and Czako are now applying their techniques to study the combustion of methane and oxygen, which produces carbon dioxide. "It's important to understand the dynamics of this reaction, because it might lead to more efficient ways to produce fuel, and a reduction in the levels of pollution emitted," Bowman says.


Story Source:

The above story is based on materials provided by Emory University. The original article was written by Carol Clark. Note: Materials may be edited for content and length.


Journal Reference:

  1. G. Czako, J. M. Bowman. Dynamics of the Reaction of Methane with Chlorine Atom on an Accurate Potential Energy Surface. Science, 2011; 334 (6054): 343 DOI: 10.1126/science.1208514

Cite This Page:

Emory University. "Chemists find new dimension to rules for reactions." ScienceDaily. ScienceDaily, 25 October 2011. <www.sciencedaily.com/releases/2011/10/111020145056.htm>.
Emory University. (2011, October 25). Chemists find new dimension to rules for reactions. ScienceDaily. Retrieved October 31, 2014 from www.sciencedaily.com/releases/2011/10/111020145056.htm
Emory University. "Chemists find new dimension to rules for reactions." ScienceDaily. www.sciencedaily.com/releases/2011/10/111020145056.htm (accessed October 31, 2014).

Share This



More Matter & Energy News

Friday, October 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Jaguar Land Rover Opens $800 Million Factory in Britain

Jaguar Land Rover Opens $800 Million Factory in Britain

AFP (Oct. 30, 2014) British luxury car manufacturer Jaguar Land Rover opened a $800 million engine manufacturing centre in western England, creating 1,400 jobs. Duration: 00:45 Video provided by AFP
Powered by NewsLook.com
SkyCruiser Concept Claims to Solve Problem With Flying Cars

SkyCruiser Concept Claims to Solve Problem With Flying Cars

Buzz60 (Oct. 30, 2014) A start-up company called Krossblade says its SkyCruiser concept flying car solves the problem with most flying car concepts. Mara Montalbano (@maramontalbano) explains. Video provided by Buzz60
Powered by NewsLook.com
Mind-Controlled Prosthetic Arm Restores Amputee Dexterity

Mind-Controlled Prosthetic Arm Restores Amputee Dexterity

Reuters - Innovations Video Online (Oct. 29, 2014) A Swedish amputee who became the first person to ever receive a brain controlled prosthetic arm is able to manipulate and handle delicate objects with an unprecedented level of dexterity. The device is connected directly to his bone, nerves and muscles, giving him the ability to control it with his thoughts. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Robots Get Funky on the Dance Floor

Robots Get Funky on the Dance Floor

AP (Oct. 29, 2014) Dancing, spinning and fighting robots are showing off their agility at "Robocomp" in Krakow. (Oct. 29) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins