the time that it takes for a bond to stretch or bend
and, perhaps, break. If we could follow atoms on that time
scale, we could make a movie of the changes in molecules as
they take part in a chemical reaction. The new fi eld of femtochemistry,
the study of very fast chemical processes, is
bringing us closer to realizing that dream. Lasers can emit
very intense but short pulses of electromagnetic radiation,
and so they can be used to study processes on very short
time scales. Recent developments have pushed the time scale
of observations toward the attosecond region (1 at 1018 s),
where even the motion of electrons is frozen.