Their work was reported in the September 2 issue of Nature . This SIMS group specializes in femtosecond laser technology, molecular dynamics and intense field physics. Modern lasers can now routinely produce pulses in this range. The Nature article describes a new femtosecond technique for following and distinguishing the electronic rearrangements and atomic motions in a molecular process, even though they occur on the same time scale. By measuring the removed electron with a technique called photoelectron spectroscopy, Dr. Albert Stolow and co-workers were able to follow both the atomic motions and the electronic rearrangements that accompany them.
Femtoseconds are the time scale for ultrafast chemical reactions and internal motions in molecules.
When a molecule is excited, both its atoms and electrons can begin to move. The electrons, being very light and fast, might easily adjust to the motions of the much heavier atoms. In many important cases, however, the electronic rearrangements and atomic motions occur on the same time scale, making it difficult to discern what is happening. Femtosecond lasers are used as an ultrafast stroboscope to watch the molecular motions as they occur. One laser pulse starts the process and a second takes a 'snapshot' at a later time.