Release date: Jan. 25, 2006
Contact: Beverly Cox Clark at 404-712-8780 or beverly.clark@emory.edu

Emory Research Helps Explain 'Scrambler' Molecule

Chemists at Emory University have helped calculate the structure of a very unusual molecule, thought to be abundant only in outer space, whose hyperactive atoms have earned it the nickname "the scrambler." This highly caustic "protonated methane," or CH5+, is also called a "super acid," and it is a short-lived player in the chemical reactions that make petroleum products.

The advance, described in the Jan. 6 issue of Science, is a step toward overcoming a decades-old challenge in chemistry to explain reactions that occur within very cold clouds among the stars, and also perhaps for developing new chemical processes.

The paper combines experiments performed by David Nesbitt and colleagues at JILA, a joint institute of the Commerce Department's National Institute of Standards and Technology (NIST) and University of Colorado at Boulder, with theoretical predictions made with Joel Bowman at Emory University and Anne McCoy at The Ohio State University.

Most molecules have a rigid three-dimensional structure. But the subject of the new study, "protonated" methane, contains one carbon atom and five hydrogen atoms, one of which is ionized, leaving nothing but a proton (a particle with a positive charge). As a result, the five protons from the hydrogen atoms scramble for four bonds around the molecule as if playing a continuous game of musical chairs.

In the process, the molecule classically vibrates and rotates in a bizarre manner, morphing between several 3D structures with nearly identical energy levels. (Animation available on the Emory University chemistry department Web site.) Chemists have spent decades trying to explain why and how this occurs, a challenge that has seemed insurmountable until recently.

To identify chemicals on earth and in outer space, scientists record the spectrum of light absorbed by a molecule. Each molecule ever identified has its own unique spectrum, resembling lines in a bar code. Since the 1960s, when petrochemical experiments suggested the existence of CH5+, scientists have been trying to record a complete spectrum of it, but the molecule won't sit still.

Bowman and McCoy helped build a theoretical model based on innovative calculations of what the motions must be, resulting in the most complete vibrational spectra of the molecule ever calculated, and creating a theoretical picture of its structure.

Bowman also had another paper published in Science on Jan. 20. The research on "Signatures of H2CO Photodissociation from Two Electronic States" analyzed the decomposition of formaldehyde (a key component of air pollution) in the atmosphere.

Emory University is known for its demanding academics, outstanding undergraduate college of arts and sciences, highly ranked professional schools and state-of-the-art research facilities. For nearly two decades Emory has been named one of the country's top 25 national universities by U.S. News & World Report. In addition to its nine schools, the university encompasses The Carter Center, Yerkes National Primate Research Center and Emory Healthcare, the state's largest and most comprehensive health care system.

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