Hydrogen molecules, femtosecond time scale

Molecular hydrogen has a vibrational period of only 7.6 fs, while vibrational modes involving heavier atoms are slower. The motions of atoms in activated molecules, the various vibrations and rotations leading to chemical reactions, will generally take place over time periods of 10 to 100 or 1000 fs, the femtosecond time scale. One femtosecond is 10 s femton is Swedish for 15, making the femtosecond unit, the next beyond the nicely classical miUi-, micro-, nano-, picosecond sequence, easy to remember. 

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