EMBARGOED FOR RELEASE UNTIL:                 Linda Joy
March 21, 1994, at 9:12 a.m. EST             (301) 975-4403

to coincide with presentations of            TN-5971
Richard R. Cavanagh, 9:12 a.m.
and J. William Gadzuk, 11 a.m.
Allegheny III, Vista Hotel
American Physical Society Meeting
Pittsburgh, Pa.


               A BLINK OF TECHNOLOGY: FEMTOSECOND CHEMISTRY
                     REDEFINING MOLECULAR INTERACTIONS


PITTSBURGH--Using ultrafast optics and lasers, physicists and
chemists are opening a portal through which they can view the
subtlest and quickest changes in atomic motions.

     Understanding these ultrasmall, ultrafast changes could lead
to new avenues for controlling chemical reactions at surfaces,
say scientists at the National Institute of Standards and
Technology.

     Speaking at the American Physical Society's annual meeting,
NIST surface scientists J. William Gadzuk and Richard R. Cavanagh
explained that the emerging field of femtosecond (quadrillionth
of a second) chemistry could enable scientists to break chemical
bonds selectively, spur reactions and choose desired products.

     "We're looking for ways to get around traditional thermal
chemistry.  We're trying to control atomic motion to get what we
want," Cavanagh said.  "It would be a more efficient way of
driving a reaction."

     Scientists are using precisely timed laser pulses to see
femtosecond changes in various parts of atoms and molecules.
Measuring the changes in femtoseconds gives scientists a glimpse
of the various stages atoms go through in a reaction. 

     Just as a photographer uses a shutter faster than his
subjects to freeze action in an Olympic race, scientists have
devised a very fast shutter based on the speed of light to
measure molecular motions.  Laser pulses, which travel
approximately a billion feet per second, can freeze action in
atoms that vibrate about as fast as sound travels.

     In femtosecond surface chemistry, light is also used to
initiate a reaction by exciting electrons.  Hot electrons so
produced can redistribute the energy of the laser pulse into 
preselected parts of the molecular surface system.

     "We're talking about being able to strip out pieces and put
them wherever you would like," explained Gadzuk.  "It's a
powerful new frontier."  Gadzuk, a theoretician in NIST's Surface
and Microanalysis Science Division, presented APS members with an
overview and history of femtosecond chemistry at surfaces with
particular emphasis on wave packet modeling carried out at NIST.

     "Much of what is today called selective femtochemistry owes
its existence to ultrafast laser technology capable of producing
pulses comparable to the time scale of molecular vibrations,"
Gadzuk said.

     Two such laser pulses can create a shutter for viewing
atomic motion.  The pulses are aimed at a sample simultaneously,
but one is delayed by mirrors and arrives at the sample shortly
after the first.  Interactions between the pulses and the sample
show how atoms in the sample changed between the first and second
pulse.  

     Cavanagh and postdoctoral researcher Thomas Germer are using
fast optics and lasers to test new femtochemistry theories. In
his APS presentation, Cavanagh described recent experiments to
test the coupling strength of bonds between carbon monoxide
molecules and copper surfaces.

     The aim of this research was to discover whether energy
localized in electrons or in atoms has a greater influence on
chemical reactions.  The NIST experiments charted very fast
temperature changes in electrons after they were struck with
photons.  They also measured how quickly the nuclei of atoms
changed temperature when struck with fast laser pulses.

     The experiments are helping scientists understand how
quickly energy is transferred between different molecules on a
surface.  Studies of the carbon monoxide and copper bonds reveal
that the temperature of both electrons and atoms influences
chemical reactions.  "Our experiments show that both are
important, occurring in a few picoseconds (trillionths of a
second)," Cavanagh said.

     Experiments such as these are helping scientists to
determine the optimal amount of light, or energy, to trigger a
chemical change.  As femtosecond chemistry reveals more about
atomic particle behavior, scientists may devise futuristic ways
of synthesizing materials or fabricating nanostructures. 

     As a non-regulatory agency of the Commerce Department's
Technology Administration, NIST promotes U.S. economic growth by
working with industry to develop and apply technology,
measurements and standards.

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