Newswise — Ohio
State University physicists have obtained the first-ever
experimental evidence of a particular quantum mechanical
effect –- one that was theorized a decade ago.
effect, called quantum monodromy (Greek for “once
around”), relates in part to the behavior of molecules
based on their atomic structure and vibrational frequencies.
A better understanding of quantum monodromy could
have implications in astronomy, atmospheric science,
The physicists reported their results at the 60th
International Symposium on Molecular Spectroscopy,
held at Ohio State University.
In some molecules, the atomic bonds act like joints
where the molecule can bend and rotate unusually
far from their normal positions, like a human arm
can bend or rotate at the elbow or shoulder, explained
Manfred Winnewisser, adjunct professor of physics
at Ohio State. The movement changes the shape of
the molecule, and affects its vibrational and rotational
energy as well as how it interacts with other molecules.
The water molecule, for instance, exhibits this
behavior, and scientists suspect that the bending
of that molecule might affect the function of water
vapor in the atmosphere.
“In order to understand the absorption of solar
radiation in the atmosphere, one has to understand
the proper physics,” Winnewisser said. “So an improved
understanding of physics or chemistry or biology
is actually the most important application of studies
To understand the movement of such molecules, scientists
draw a graph, a kind of map of the molecule's energy.
For molecules that exhibit quantum monodromy, the
map looks like an upright cylinder with a bulge rising
from the bottom, like the bottom of a wine or champagne
The top of the bulge is a critical point where the
shape of the molecule changes, Winnewisser said.
learn more about what happens at this “monodromy
point,” the Ohio State physicists studied the molecule
cyanogen isothiocyanate (NCNCS). Its atoms fit together
in a long chain that they hoped would exhibit the
bending they wanted to see.
A special laboratory instrument enabled the test.
Frank De Lucia, professor of physics at Ohio State,
and his colleagues designed the instrument to utilize
their FAst Scan Submillimeter Spectroscopy Technique
The technique offers a quick way for scientists
to examine the spectrum of electromagnetic radiation
absorbed by a molecule. Each molecule has its own
one-of-a-kind spectral pattern, like lines in a bar
code. FASSST takes a quick scan of a wide range of
spectral wavelengths, so scientists can easily recognize
the pattern of the molecule they are looking for.
In the case of the NCNCS molecule, Winnewisser and
his colleagues used FASSST to record a series of
spectral features, including the features corresponding
to the energy of the molecule at the monodromy point.
Ivan Medvedev, a doctoral student in physics, and
his colleagues, then used software he developed to
reveal patterns in the spectrum. The open-source
software, called Computer Aided Assignment of Asymmetric
Rotor Spectra (CAAARS), is available for download
from Medvedev's Web page ( http://www.physics.ohio-state.edu/~medvedev/caaars.htm ).
When they plotted the spectrum with CAAARS, the
physicists could identify patterns that exactly matched
patterns in the predicted spectrum for a molecule
exhibiting quantum monodromy.
Other team members on this project included Brenda
Winnewisser, also adjunct professor, and Markus Behnke,
a postdoctoral researcher, both of the Ohio State
Department of Physics, and Stephen Ross, professor
of physics at the University of New Brunswick in