Andrew Yee
January 6th 06, 05:19 PM
National Institute of Standards and Technology
CONTACT:
Laura Ost, (301) 975-4034
FOR IMMEDIATE RELEASE: Jan. 5, 2006
Experiments Help Explain Mysterious 'Floppy' Space Molecule
Boulder, Colo. -- A laboratory method developed for making and analyzing
cold, concentrated samples of a mysterious "floppy" molecule thought to be
abundant only in outer space has revealed new data that help explain the
molecule's properties.
The advance, described in the Jan. 6 issue of Science, is a step toward
overcoming a decades-old challenge in chemistry -- explaining reactions
that occur within very cold clouds among the stars, and 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 in Atlanta, Ga., and Anne McCoy
at The Ohio State University in Columbus, Ohio.
Most molecules have a rigid three-dimensional (3D) structure. The subject
of the new study is "protonated" methane, which contains one carbon atom
and five hydrogen atoms, one of which is ionized, leaving nothing but a
proton (a particle with a positive charge). 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 at
<http://www.nist.gov/public_affairs/images/floppy_animation.htm>.)
Chemists have spent decades trying to explain why and how this occurs, a
challenge that has seemed insurmountable until recently.
Protonated methane is a so-called "super acid." This class of molecule has
been shown to be more than a million times more powerful than conventional
acids and is more effective in inducing reactions that produce solvents
and many other important industrial products.
Many theories have been published on the puzzling behavior of this charged
molecule (or ion), but experiments must be done to match the ion's energy
characteristics with its physical motions, and such data are difficult to
collect and understand. In particular, scientists are interested in how
the molecule absorbs different wavelengths of infrared (IR) light, which
provides clues about nuclear motion and chemical bonds and structures.
The JILA method generates concentrated amounts of the ion at cold enough
temperatures to simplify the complex IR spectrum so it can be analyzed.
The data strike a balance between detail and simplicity, providing useful
information that is still challenging but easier to understand than ever
before. This enabled the authors of the Science paper to match predicted
changes in energy to specific vibrations and partially characterize the
ion's structure and dynamics. For example, they were able to correlate one
intense spectral feature to a transition between two 3D structures with
equivalent energy levels.
Previously published spectra of this molecule have either been too low
resolution to "see" this motion, or too hot (and therefore too complex) to
analyze.
"The experiments have provided the first jet-cooled, high-resolution
spectrum of this highly fluxional molecule," says Nesbitt, a NIST Fellow
who led the JILA experimental team. "This has been among the most
sought-after IR spectra since the first appearance of this molecule in
mass spectrometers over 50 years ago. This is a problem that has occupied
many careers; every piece helps."
The JILA method involves making methane gas at high temperature and
pressure, and expanding it into a vacuum to cool the molecules to 10 K
(-442 degrees F). The cold molecules then file through an opening just 1
millimeter wide, where they are hit with a "lightning bolt" of electrical
current that generates high concentrations of highly reactive ions. The
key to mass production is to surround the molecules with enough electrons
to make the entire gas mixture neutral in charge, Nesbitt says.
For the analysis step, JILA scientists shine an infrared laser on the cold
ions, and detect the light that passes through. The light that is lost, or
the small amount absorbed by the molecules, is analyzed to obtain a
pattern of absorption at different wavelengths. The technique is very
sensitive, thanks to methods for detecting trace absorption of the laser
light and manipulating the electrical discharge to maximize the ion
concentration levels.
Future and ongoing studies will focus on matching the ion's IR absorption
characteristics with its rotational structure, including end-over-end
tumbling. "Protonated methane still has a few tricks up its sleeve,"
Nesbitt cautions.
The research was supported in part by the National Science Foundation,
Office of Naval Research, and Air Force Office of Scientific Research.
As a non-regulatory agency of the Commerce Department's Technology
Administration, NIST promotes U.S. innovation and industrial
competitiveness by advancing measurement science, standards and technology
in ways that enhance economic security and improve our quality of life.
X. Huang, A.B. McCoy, J.M. Bowman, L.M. Johnson, C. Savage, F. Dong,
and D.J. Nesbitt. 2005. "Quantum deconstruction of the infrared spectrum
of CH5+". Science. Jan. 6.
IMAGE CAPTION:
[http://www.nist.gov/public_affairs/images/05PHY024_Floppy_NesbittGrpHR.jpg
(3.8MB)]
A research team at JILA has developed a new method for making and
analyzing an unusual floppy molecule. Shown above with their experimental
apparatus are (from left) Chandra Savage, Erin Whitney, Feng Dong, and
David Nesbitt.
Photo by Jeff Fal, University of Colorado, Boulder
*****
Research Communications
Ohio State University
Contact:
Anne B. McCoy, (614) 292-9694; mccoy.154 @ osu.edu
Written by:
Pam Frost Gorder, (614) 292-9475
Embargoed until 2:00 p.m. ET, Thursday, January 5, 2006, to coincide with
publication in the journal Science.
CHEMISTS CALCULATE STRUCTURE OF PUZZLING "SCRAMBLER" MOLECULE
COLUMBUS, Ohio -- Chemists have calculated the structure of a very unusual
molecule, one 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.
CH5+ should also be present in interstellar clouds where stars and planets
form, said Anne B. McCoy, professor of chemistry at Ohio State University.
McCoy hopes that the work she and her team are publishing in the current
issue of the journal Science will one day give astronomers the tools they
need to determine once and for all whether the molecule is really out
there in space.
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. Scientists who tried to image CH5+ have
found that it's like a three-year-old child -- impossible to photograph,
except in a blur.
"CH5+ has five hydrogen atoms scrambling around a carbon atom that sits at
the center," McCoy explained. The hydrogen atoms are simultaneously
rotating and vibrating.
Because the atoms are always on the move, scientists have difficulty
interpreting the spectrum. Still, they have recorded several CH5+ spectra
experimentally.
Study coauthors David Nesbitt, Chandra Savage, and Feng Dong of JILA, a
joint research institute of the University of Colorado at Boulder and the
National Institute of Standards and Technology, report the most recent and
best resolved of these spectra to date in the Science paper. But in spite
of this progress, researchers have not been able to match the lines in the
CH5+ bar code to any specific motions of the molecule.
That's what McCoy and Professor Joel M. Bowman of Emory University did
mathematically. For certain features on the spectrum, they calculated what
the motions must be.
The result is most complete vibrational spectra ever calculated -- a
theoretical picture of the molecule's structure.
The chemists' employed a unique strategy in their calculations.
"Although the hydrogen atoms are constantly scrambling, the overall range
of types of structures can be characterized by three basic
configurations," McCoy said. One configuration corresponds to a low energy
state for the molecule, and the other two to higher energy states. McCoy,
Bowman, Ohio State graduate student Lindsay M. Johnson and Emory
postdoctoral researcher Xinchuan Huang calculated spectra for all three
structures.
That in itself was standard procedure, she said -- but then they went on
to examine the probability that the molecule would assume each of those
three structures, and used that information to weight their calculations.
"It turns out that this was the crucial step," McCoy said.
She acknowledged that her team hasn't yet assembled a full picture of
CH5+, since their calculations accounted for the vibration of the molecule
but not its constant rotation. That will be their next step. If
successful, they'll have a complete theoretical view of what the
molecule's spectrum should look like.
"The ultimate goal of this work is to identify a kind of signature for
CH5+," McCoy said. "Once we have it, we can compare it to what is observed
from astronomical measurements to determine its abundance in different
regions of space."
"From a more fundamental perspective, one thing that intrigues me is how
we can characterize molecules like CH5+ that have no single well-defined
structure and how this lack of a well-defined structure impacts its
reactivity," she continued.
She and her coauthors have started calculating what would happen when the
hydrogen atoms in CH5+ are replaced with deuterium, also known as "heavy
hydrogen." They suspect that adding one or two heavy hydrogen atoms will
stabilize the remaining hydrogen atoms and settle "the scrambler" down
once and for all.
CONTACT:
Laura Ost, (301) 975-4034
FOR IMMEDIATE RELEASE: Jan. 5, 2006
Experiments Help Explain Mysterious 'Floppy' Space Molecule
Boulder, Colo. -- A laboratory method developed for making and analyzing
cold, concentrated samples of a mysterious "floppy" molecule thought to be
abundant only in outer space has revealed new data that help explain the
molecule's properties.
The advance, described in the Jan. 6 issue of Science, is a step toward
overcoming a decades-old challenge in chemistry -- explaining reactions
that occur within very cold clouds among the stars, and 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 in Atlanta, Ga., and Anne McCoy
at The Ohio State University in Columbus, Ohio.
Most molecules have a rigid three-dimensional (3D) structure. The subject
of the new study is "protonated" methane, which contains one carbon atom
and five hydrogen atoms, one of which is ionized, leaving nothing but a
proton (a particle with a positive charge). 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 at
<http://www.nist.gov/public_affairs/images/floppy_animation.htm>.)
Chemists have spent decades trying to explain why and how this occurs, a
challenge that has seemed insurmountable until recently.
Protonated methane is a so-called "super acid." This class of molecule has
been shown to be more than a million times more powerful than conventional
acids and is more effective in inducing reactions that produce solvents
and many other important industrial products.
Many theories have been published on the puzzling behavior of this charged
molecule (or ion), but experiments must be done to match the ion's energy
characteristics with its physical motions, and such data are difficult to
collect and understand. In particular, scientists are interested in how
the molecule absorbs different wavelengths of infrared (IR) light, which
provides clues about nuclear motion and chemical bonds and structures.
The JILA method generates concentrated amounts of the ion at cold enough
temperatures to simplify the complex IR spectrum so it can be analyzed.
The data strike a balance between detail and simplicity, providing useful
information that is still challenging but easier to understand than ever
before. This enabled the authors of the Science paper to match predicted
changes in energy to specific vibrations and partially characterize the
ion's structure and dynamics. For example, they were able to correlate one
intense spectral feature to a transition between two 3D structures with
equivalent energy levels.
Previously published spectra of this molecule have either been too low
resolution to "see" this motion, or too hot (and therefore too complex) to
analyze.
"The experiments have provided the first jet-cooled, high-resolution
spectrum of this highly fluxional molecule," says Nesbitt, a NIST Fellow
who led the JILA experimental team. "This has been among the most
sought-after IR spectra since the first appearance of this molecule in
mass spectrometers over 50 years ago. This is a problem that has occupied
many careers; every piece helps."
The JILA method involves making methane gas at high temperature and
pressure, and expanding it into a vacuum to cool the molecules to 10 K
(-442 degrees F). The cold molecules then file through an opening just 1
millimeter wide, where they are hit with a "lightning bolt" of electrical
current that generates high concentrations of highly reactive ions. The
key to mass production is to surround the molecules with enough electrons
to make the entire gas mixture neutral in charge, Nesbitt says.
For the analysis step, JILA scientists shine an infrared laser on the cold
ions, and detect the light that passes through. The light that is lost, or
the small amount absorbed by the molecules, is analyzed to obtain a
pattern of absorption at different wavelengths. The technique is very
sensitive, thanks to methods for detecting trace absorption of the laser
light and manipulating the electrical discharge to maximize the ion
concentration levels.
Future and ongoing studies will focus on matching the ion's IR absorption
characteristics with its rotational structure, including end-over-end
tumbling. "Protonated methane still has a few tricks up its sleeve,"
Nesbitt cautions.
The research was supported in part by the National Science Foundation,
Office of Naval Research, and Air Force Office of Scientific Research.
As a non-regulatory agency of the Commerce Department's Technology
Administration, NIST promotes U.S. innovation and industrial
competitiveness by advancing measurement science, standards and technology
in ways that enhance economic security and improve our quality of life.
X. Huang, A.B. McCoy, J.M. Bowman, L.M. Johnson, C. Savage, F. Dong,
and D.J. Nesbitt. 2005. "Quantum deconstruction of the infrared spectrum
of CH5+". Science. Jan. 6.
IMAGE CAPTION:
[http://www.nist.gov/public_affairs/images/05PHY024_Floppy_NesbittGrpHR.jpg
(3.8MB)]
A research team at JILA has developed a new method for making and
analyzing an unusual floppy molecule. Shown above with their experimental
apparatus are (from left) Chandra Savage, Erin Whitney, Feng Dong, and
David Nesbitt.
Photo by Jeff Fal, University of Colorado, Boulder
*****
Research Communications
Ohio State University
Contact:
Anne B. McCoy, (614) 292-9694; mccoy.154 @ osu.edu
Written by:
Pam Frost Gorder, (614) 292-9475
Embargoed until 2:00 p.m. ET, Thursday, January 5, 2006, to coincide with
publication in the journal Science.
CHEMISTS CALCULATE STRUCTURE OF PUZZLING "SCRAMBLER" MOLECULE
COLUMBUS, Ohio -- Chemists have calculated the structure of a very unusual
molecule, one 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.
CH5+ should also be present in interstellar clouds where stars and planets
form, said Anne B. McCoy, professor of chemistry at Ohio State University.
McCoy hopes that the work she and her team are publishing in the current
issue of the journal Science will one day give astronomers the tools they
need to determine once and for all whether the molecule is really out
there in space.
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. Scientists who tried to image CH5+ have
found that it's like a three-year-old child -- impossible to photograph,
except in a blur.
"CH5+ has five hydrogen atoms scrambling around a carbon atom that sits at
the center," McCoy explained. The hydrogen atoms are simultaneously
rotating and vibrating.
Because the atoms are always on the move, scientists have difficulty
interpreting the spectrum. Still, they have recorded several CH5+ spectra
experimentally.
Study coauthors David Nesbitt, Chandra Savage, and Feng Dong of JILA, a
joint research institute of the University of Colorado at Boulder and the
National Institute of Standards and Technology, report the most recent and
best resolved of these spectra to date in the Science paper. But in spite
of this progress, researchers have not been able to match the lines in the
CH5+ bar code to any specific motions of the molecule.
That's what McCoy and Professor Joel M. Bowman of Emory University did
mathematically. For certain features on the spectrum, they calculated what
the motions must be.
The result is most complete vibrational spectra ever calculated -- a
theoretical picture of the molecule's structure.
The chemists' employed a unique strategy in their calculations.
"Although the hydrogen atoms are constantly scrambling, the overall range
of types of structures can be characterized by three basic
configurations," McCoy said. One configuration corresponds to a low energy
state for the molecule, and the other two to higher energy states. McCoy,
Bowman, Ohio State graduate student Lindsay M. Johnson and Emory
postdoctoral researcher Xinchuan Huang calculated spectra for all three
structures.
That in itself was standard procedure, she said -- but then they went on
to examine the probability that the molecule would assume each of those
three structures, and used that information to weight their calculations.
"It turns out that this was the crucial step," McCoy said.
She acknowledged that her team hasn't yet assembled a full picture of
CH5+, since their calculations accounted for the vibration of the molecule
but not its constant rotation. That will be their next step. If
successful, they'll have a complete theoretical view of what the
molecule's spectrum should look like.
"The ultimate goal of this work is to identify a kind of signature for
CH5+," McCoy said. "Once we have it, we can compare it to what is observed
from astronomical measurements to determine its abundance in different
regions of space."
"From a more fundamental perspective, one thing that intrigues me is how
we can characterize molecules like CH5+ that have no single well-defined
structure and how this lack of a well-defined structure impacts its
reactivity," she continued.
She and her coauthors have started calculating what would happen when the
hydrogen atoms in CH5+ are replaced with deuterium, also known as "heavy
hydrogen." They suspect that adding one or two heavy hydrogen atoms will
stabilize the remaining hydrogen atoms and settle "the scrambler" down
once and for all.