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.

“Shocking” 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.

The World’s 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.

How Do Explosives React to “Insults?”
A 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.

Chemistry 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.

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