2000: Atomic motions deciphered
Femtochemistry comes of age.1 Molecular dynamics is routinely captured via femtosecond light pulses.
When scientists started to „take pictures“ of the movements of atoms in molecules during chemical reactions at the end of the 1980s, this had little to do with conventional photography. The basic principle, however, remained the same: A short exposure time was needed to »freeze« the dynamics under scrutiny and display changes of the microscopic states of matter in a series of snapshots taken at different instant during the evolution of the system. The atomic composition and/or structure of molecules can change within femtoseconds, i.e. within millionths of a billionth of a second. The required ultrashort exposure time was provided by femtosecond laser pulses.
The 1999 Nobel Prize in Chemistry honoured the pioneering contributions of Prof. Ahmed Zewail from CALTECH to establishing femtochemistry, permitting the observation of changes in the atomic structure and/or composition of molecules in real time. In spite of these breathtaking advances, several mysteries remained unresolved.
How do the electrons move prior to changes in atomic structure and how does initial electron dynamics influence the fate of the molecule? How does electron-nuclear coupling affect reaction pathways? Answers to them called for even faster techniques, reaching out into the attosecond domain, the characteristic time scale of electronic motions at the atomic scale.