New light cast on key chemical reactions in interstellar space
ARGONNE, Ill. (July 10, 2007) – A detailed understanding of key chemical reactions
that take place in interstellar space has been provided by groundbreaking
research at two U.S. Department of Energy national laboratories and
two European universities.
Argonne National Laboratory senior chemist Stephen Klippenstein – along with
colleagues at Sandia National
Laboratories; the Institute of Physics, University
of Rennes, France; and the
University of Cambridge, U.K. – has developed
a detailed understanding of the dynamics of reactions between neutral radicals
and neutral molecules, known as “neutral-neutral” reactions, at temperatures
as low as 20 Kelvin, approximately the temperature of interstellar space.
In their work, Klippenstein and his collaborators determined why certain molecules
reacted rapidly even at low temperatures by carefully comparing theory and
experiment for a sample class of reactions (O3P + alkenes) that spans the
range from non-reactive to highly reactive. The observed results from the experiment
closely correlated with theoretical predictions, said Klippenstein.
“It was
remarkable," he said, "just how well theory and experiment agreed
throughout the whole spectrum from 20 Kelvin to room temperature. This means
that we can rely on theory to predict which reactions will happen quickly.”
Establishing a working model for interstellar chemistry is especially important
given the difficulty of performing large-scale experiments, according to Klippenstein.
“My
collaborators have developed some great experimental techniques for measuring
these reactions at low temperatures," he said. "But such experiments
are still very time-consuming and are also hard to apply to many reactions.
So schemes for predicting the reactivity for arbitrary reactions, either a
priori or from extrapolation of measurements at higher temperatures,
are of great utility to modelers of interstellar chemistry.”
Prior experimental studies with the CRESU (Reaction Kinetics in Uniform Supersonic
Flow) technique demonstrated that a “surprising number” of neutral-neutral
reactions remain rapid at very low temperatures. As a result, such reactions
can play an important role in the chemistry of interstellar space, in contrast
with the conventional wisdom that interstellar chemistry is essentially all
ion-based.
The paper, entitled “Understanding
Reactivity at Very Low Temperatures: The Reactions of Oxygen Atoms with Alkenes,” appears
in the July 6 issue of Science.
This research was supported by the Division of Chemical
Sciences, Geosciences and Biosciences within the Office of Basic Energy Sciences of the U.S. Department
of Energy.
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For more information, please
contact Steve McGregor (630/252-5580 or media@anl.gov)
at Argonne.
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