Scientists at the National Research Council of Canada have developed a technique that allows them to follow the ultrafast internal processes that lead to electronic-structural rearrangements in molecules. This discovery, which may eventually provide insights into the new field of ?molecular electronics? and biologicial processes such as vision and photosynthesis, was made by a multidisciplinary team of physicists and chemists at NRC?s Steacie Institute for Molecular Sciences (SIMS). 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. A femtosecond (10-15 s) is an extremely short duration: one femtosecond is to one minute as one minute is to the age of the universe. 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. The idea is to use ionization (removal of an electron) to get a picture of what the molecule was doing at the moment of ionization. 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
Contact: Dr. Albert Stolow
National Research Council of Canada