A technique could pave the way for imaging electron behaviour as chemical reactions happen.

Many reactions are governed by the behaviour of electrons in excited orbital states, but these states are difficult to capture because they last only a few picoseconds (10−12 seconds). Now, Masahiko Takahashi at Tohoku University in Sendai, Japan, and his colleagues have measured the excited states of molecules of acetone gas by probing them with ultrashort pulses of electrons.

Electrons in the pulse knocked excited electrons out of the atoms comprising the acetone. By simultaneously measuring the energy of the ejected electrons and those from the pulse, the team determined the energy and momentum of the molecule's excited state, which lasted for just 13.5 picoseconds.

Although the data quality is currently low, the results show that such measurements are feasible, say the authors.

Phys. Rev. Lett. 114, 103005 (2015)