Subscribe to our free daily newsletters
. 24/7 Space News .

Subscribe to our free daily newsletters

MIT chemists characterize a chemical state thought to be unobservable
by Staff Writers
Boston MA (SPX) Dec 14, 2015

MIT chemists calculated the energy required for a molecule of acetylene in the U-shaped conformation to reach the transition state. Once that state is reached, the reaction proceeds to completion and acetylene takes on a zig-zag conformation. Image courtesy of the researchers.

For the first time, MIT chemists have measured the energy of the transition state of a chemical reaction - a fleeting, unstable state that is a reaction's point of no return.

Chemists have long believed it impossible to experimentally characterize transition states, but the MIT team achieved it by analyzing changes in the patterns of vibrational energy levels in reactants approaching the transition state.

"This was supposed to be impossible because of the intrinsic complexity, but we found the magic decoder that enables us to go deeper into this regime," says Robert Field, the Robert T. Haslam and Bradley Dewey Professor of Chemistry and senior author of the study, which appears in the Dec. 10 online edition of Science.

Broken patterns
As every freshman chemistry student learns, the transition state of a reaction is the gateway between reactants and products. Most reactions require an input of energy, known as the activation energy, to reach the transition state.

"Your reactants and products are stable valleys on either side of a mountain range, and the transition state is the pass. It's the most convenient way to get from one to the other," says Josh Baraban, the paper's lead author and a former MIT graduate student who is now a research associate at the University of Colorado Boulder. "Because it only exists as you go from as one thing to another, it's never really been thought of as something that you can easily study directly."

Field, Baraban, and their colleagues investigated a type of reaction known as an isomerization, in which a molecule undergoes a change of shape. They focused on acetylene, a molecule consisting of two carbon atoms bound to each other, each with one hydrogen atom attached to it. Field's lab has long studied the isomerization of the most stable linear form of acetylene to an isomer called vinylidene.

In this work, which focused on an excited electronic state of acetylene, the molecule converts from a U-shaped conformation, in which both hydrogen atoms are above the carbon-carbon bond, to a zigzag conformation, in which one hydrogen atom is above and the other is below.

The MIT team used tunable laser spectroscopy to monitor changes in the vibrations of the acetylene molecules as the researchers added more energy to the system. Ordinarily, molecules vibrate at frequencies that evolve in a predictable pattern with increasing energy. From these patterns, the researchers can infer the vibrational motion of the molecules at each energy level.

As the researchers systematically explored increasing energy levels, they observed the predicted patterns until the molecules reached a certain and carefully chosen internal energy arrangement. At this point the patterns broke down and the molecules exhibited vibrations at significantly lower frequencies than expected.

"We realized that where we saw the patterns breaking specifically involved the vibrations that were related to the kind of structural changes that should be happening" at the transition state between these two conformations, Baraban says. "It looks exactly like what you'd expect."

The researchers also devised a formula that allows them to determine the energy of the transition state. This result is important for predictions based on the Arrhenius equation, which describes how temperature affects chemical reaction rates.

Other reactions
In this study, the team also used this technique to accurately predict the transition-state structure and energy of the isomerization of hydrogen cyanide (HCN) to hydrogen isocyanide (HNC). When this happens, a hydrogen atom originally bound to carbon gets passed to nitrogen.

Although they focused on isomerization reactions in this study, the researchers believe that this approach could in principle also be applied to any other reaction that must overcome an energy barrier. Analyzing complex reactions such as those where two molecules come together or one molecule breaks into two should be possible but would be more technically challenging, they say.

Other authors of the Science paper are former MIT undergraduate Bryan Changala; Georg Mellau, a professor at Justus Liebig University Giessen in Germany; John Stanton, a professor at the University of Texas at Austin; and Anthony Merer, a professor at the University of British Columbia and the Institute for Atomic and Molecular Science in Taiwan.

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only


Related Links
Massachusetts Institute of Technology
Space Technology News - Applications and Research

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Previous Report
A sticky breakthrough makes for practical underwater glue
Santa Barbara CA (SPX) Dec 12, 2015
In an important step toward creating a practical underwater glue, researchers at UC Santa Barbara have designed a synthetic material that combines the key functionalities of interfacial mussel foot proteins, creating a single, low-molecular-weight, one-component adhesive. Their findings appear in the journal Nature Communications. "We have successfully mimicked the biological adhesiv ... read more

Gaia's sensors scan a lunar transit

SwRI scientists explain why moon rocks contain fewer volatiles than Earth's

All-female Russian crew starts Moon mission test

Russian moon mission would need 4 Angara-A5V launches

Mars Mission Team Addressing Vacuum Leak on Key Science Instrument

Letter to Mars? Royal Mail works it out for British boy, 5

European payload selected for ExoMars 2018 surface platform

ExoMars has historical, practical significance for Russia, Europe

Australia seeks 'ideas boom' with tax breaks, visa boosts

A Year After Maiden Voyage, Orion Progress Continues

NASA's Work to Understand Climate: A Global Perspective

Orion's power system to be put to the test

China's indigenous SatNav performing well after tests

China launches Yaogan-29 remote sensing satellite

China's scientific satellites to enter uncharted territory

China to launch Dark Matter Satellite in mid-December

Exp 45 set to return from space station

Getting Into the Flow on the ISS

Orbital to fly first space cargo mission since 2014 explosion

Russian-US Space Collaboration Intact Despite Chill in Bilateral Ties

45th Space Wing supports NASA's Orbital ATK CRS-4 launch

Orbital cargo ship blasts off toward space station

Virgin Galactic Welcomes 'Cosmic Girl' To Fleet Of Space Access Vehicles

DXL-2: Studying X-ray emissions in space

What kinds of stars form rocky planets

Half of Kepler's giant exoplanet candidates are false positives

Exiled exoplanet likely kicked out of star's neighborhood

Neptune-size exoplanet around a red dwarf star

Colombian eco-designer finds beauty in trash

Penn researchers make thinnest plates that can be picked up by hand

A sticky breakthrough makes for practical underwater glue

Conductor turned insulator amid disorder

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement