Interstellar Chemistry Gets More Complex With New Charged-Molecule Discovery (Forwarded)

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David Aguilar, CfA
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July 23, 2007

Interstellar Chemistry Gets More Complex With New Charged-Molecule Discovery

Astronomers using data from the National Science Foundation's Robert C. Byrd
Green Bank Telescope (GBT) have found the largest negatively-charged
molecule yet seen in space. The discovery of the third negatively-charged
molecule, called an anion, in less than a year and the size of the latest
anion will force a drastic revision of theoretical models of interstellar
chemistry, the astronomers say.

"This discovery continues to add to the diversity and complexity that is
already seen in the chemistry of interstellar space," said Anthony J.
Remijan of the National Radio Astronomy Observatory (NRAO). "It also adds to
the number of paths available for making the complex organic molecules and
other large molecular species that may be precursors to life in the giant
clouds from which stars and planets are formed," he added.

Two teams of scientists found negatively-charged octatetraynyl, a chain of
eight carbon atoms and one hydrogen atom, in the envelope of gas around an
old, evolved star and in a cold, dark cloud of molecular gas. In both cases,
the molecule had an extra electron, giving it a negative charge. About 130
neutral and about a dozen positively-charged molecules have been discovered
in space, but the first negatively-charged molecule was not discovered until
late last year. The largest previously-discovered negative ion found in
space has six carbon atoms and one hydrogen atom.

"Until recently, many theoretical models of how chemical reactions evolve in
interstellar space have largely neglected the presence of anions. This can
no longer be the case, and this means that there are many more ways to build
large organic molecules in cosmic environments than have been explored,"
said Jan M. Hollis of NASA's Goddard Space Flight Center (GSFC).

Ultraviolet light from stars can knock an electron off a molecule, creating
a positively-charged ion. Astronomers had thought that molecules would not
be able to retain an extra electron, and thus a negative charge, in
interstellar space for a significant time. "That obviously is not the case,"
said Mike McCarthy of the Harvard-Smithsonian Center for Astrophysics.
"Anions are surprisingly abundant in these regions."

Remijan and his colleagues found the octatetraynyl anions in the envelope of
the evolved giant star IRC +10 216, about 550 light-years from Earth in the
constellation Leo. They found radio waves emitted at specific frequencies
characteristic of the charged molecule by searching archival data from the
GBT, the largest fully-steerable radio telescope in the world.

Another team from the Harvard-Smithsonian Center for Astrophysics (CfA)
found the same characteristic emission when they observed a cold cloud of
molecular gas called TMC-1 in the constellation Taurus. These observations
also were done with the GBT. In both cases, preceding laboratory experiments
by the CfA team showed which radio frequencies actually are emitted by the
molecule, and thus told the astronomers what to look for.

"It is essential that likely interstellar molecule candidates are first
studied in laboratory experiments so that the radio frequencies they can
emit are known in advance of an astronomical observation," said Frank Lovas
of the National Institute of Standards and Technology (NIST).

Both teams announced their results in the July 20 edition of the
Astrophysical Journal Letters.

"With three negatively-charged molecules now found in a short period of
time, and in very different environments, it appears that many more probably
exist. We believe that we can discover more new species using very sensitive
and advanced radio telescopes such as the GBT, once they have been
characterized in the laboratory," said Sandra Bruenken of the CfA.

"Further detailed studies of anions, including astronomical observations,
laboratory studies, and theoretical calculations, will allow us to use them
to reveal new information about the physical and chemical processes going on
in interstellar space," said Martin Cordiner, of Queen's University in
Belfast, Northern Ireland.

"The GBT continues to take a leading role in discovering, identifying and
mapping the distribution of the largest molecules ever found in astronomical
environments and will continue to do so for the next several decades," said
Phil Jewell of NRAO.

In addition to Hollis, Lovas, Cordiner and Jewell, Remijan worked with Tom
Millar of Queen's University in Belfast, Northern Ireland, and Andrew
Markwick-Kemper of the University of Manchester in the UK.

Bruenken worked with McCarthy, Harshal Gupta, Carl Gottlieb, and Patrick
Thaddeus, all of the Harvard-Smithsonian Center for Astrophysics.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics is a joint collaboration between the Smithsonian Astrophysical
Observatory and the Harvard College Observatory. CfA scientists, organized
into six research divisions, study the origin, evolution and ultimate fate
of the universe.

[NOTE: An image supporting this release is available at
http://www.nrao.edu/pr/2007/biganion/graphics.shtml ]