Following a chemical reaction using high harmonic spectroscopy

Chemical reaction using high harmonic spectroscopy is reported. In high-harmonic spectroscopy based on recollision, we show that this apparent limitation becomes a major advantage due to the coherent nature of attosecond pulse generation. The unexcited molecules act as a local oscillator against which the dynamics is observed. Combined with the transient grating technique, we reconstruct the amplitude and phase of the excited state emission. Amplitude encodes the internuclear separation by interference at short times and scattering of the recollision electron at longer times. Phase records the attosecond dynamics of the electrons, giving access to the evolving ionisation potentials and the electronic structure of the transient molecule.