Collisions, vibrations, rotations,
and the absorption and emission of light are dynamic processes that produce
chemical reactions. Exploring these processes leads to a deeper understanding
of chemistry and to new ways of controlling chemical behavior. It also
contributes to finding solutions to problems that touch on both basic
science and national interest. Los Alamos researchers are exploring chemistry
that will help ensure the security of the nuclear stockpile. Novel experiments
will provide a fundamental understanding of how explosives detonate and
how shock waves propagate through metals. One team of researchers is creating
nanopaticles that will allow development of a new class of lasers, while
another is examining the chemistry and fate of atmospheric pollutants.
These and many other projects within the division make the field as active
and rapidly changing as the forces it studies.
Explosives and Metals
Chemistry, Dynamic Experimentation, and Applied Physics Divisions collaborate
on the HERCULES Project (for High Explosives Reaction Chemistry via Ultrafast
Laser Spectroscopy) to develop diagnostic tools for new research into
the way shock waves interact with explosives and metals. One of these
highly specialized tools takes advantage of interferometry
to probe into the realm of shock physics. Interferometry uses interference
patterns from overlapping pulses of laser light to collect information
in both space and time. The propagation of shock waves through solids
can be examined at scales of tens of nanometers and over times as small
as 10(13) of a second. Other ultrafast spectroscopic techniques
are being developed that can detect energy transfer and bond breaking
in shocked explosive materials. The information gathered provides insight
into the physics and chemistry of explosions and is important to the Laboratory's
stockpile stewardship mission and the weapons program. At right:
A shockwave moves through a 1 micrometer aluminum film in seconds.
Worlds Smallest Laser Coherent Light from Quantum Dots
Chemists at Los Alamos have created quantum-scale materials that can lase
(emit coherent light) and are made of uniformly sized pieces of semiconductor
called quantum dots. Although quantum dots have been studied for a decade,
making them lase has been an elusive goal and was only achieved by packing
them closely together. The discovery that quantum dots can lase opens
up a new field of laser technology. It enables the development of new,
inexpensive, tunable semiconductor lasers that could have applications
in such diverse fields as medicine and environmental analysis. In collaboration
with colleagues at the Massachusetts Institute of Technology, Los Alamos
researchers have developed a technique that uses cadmium selenide to make
dots between 2 and 8 nanometers in diameter.
Do Explosives React to Insults?
joint project between Chemistry and Dynamic Experimentation divisions
is aimed at unraveling the way in which explosives work at a chemical
and physical level when they are subjected to extreme conditions known
as insults. If a warhead is dropped, what happens to the explosive inside?
How do explosives react when they are exposed to fire? Knowing the answers
to such questions is important to the Departments of Defense and Energy
and to industry.
Using second harmonic generation
(SHG) microscopy, researchers have been able to look at the way high explosives
change form just before they detonate. With this technique, the explosives'
crystals were clearly shown to have shifted phase (from beta to delta)
just before detonation, when they were subjected to mechanical or thermal
insults. The green highlights in the SHG image at right show the phase
change that occurs as the insult is being applied.
on Ice Quasi-liquid Layers
Coined by Faraday in the 19th century, quasi-liquid is a term describing
liquid-like layers that form on solid surfaces at temperatures below the
solid's melting point. The layers that form on atmospheric ice particles
and in the world's snow pack affect the chemistry of those systems and
have far-reaching environmental implications. Thus, from being a mere
scientific curiosity, the study of these layers has become an inquiry
into the mechanisms that drive global change. Preliminary results suggest
that both the uptake of organic compounds in snow and the chemistry of
tropospheric ozone are affected by the presence of quasi-liquid layers.
By studying quasi-liquids in the laboratory with optical techniques, Los
Alamos chemists have been able to develop a thermo-dynamic model that
predicts the total quasi-liquid volume in the atmosphere and in the snow
pack. Their research will lead to a greater understanding of some of the
most important and ubiquitous chemical systems on earth.
Left: The Los Alamos model suggests that quasi-liquids form in multilayered
islands on ice surfaces below the triple point, where solid, liquid, and
vapor are in equilibrium.
Right: Ice crystals change from cubic form to hexagonal near 160 K.
SHG data supports the Los Alamos model by showing signal for quasi-liquid
layers starting at about 212 K and increasing through the melting point.