Abstract
We report, to the best of our knowledge, the first time-resolved high-harmonic spectroscopy (TR-HHS) study of a chemical bond rearrangement. We investigate the transient change of the high-harmonic signal from 1,3-cyclohexadiene (CHD), which undergoes ring-opening and isomerizes to 1,3,5-hexatriene (HT) upon photoexcitation. By associating the variation in the harmonic yield to the changes in the electronic state and vibrational frequencies of the molecule due to isomerization, we find that the CHD excited via two-photon absorption of 3.1 eV photons isomerizes to HT, i.e., ring-opening occurs, around 400 fs after the excitation. The present results demonstrate that TR-HHS, which can track both electronic and nuclear dynamics, is a powerful tool for studying ultrafast photochemical reactions.
Highlights
High-harmonic generation (HHG) is a result of interactions between a freed electron and its parent ion, occurring under strong laser fields [1]
This technique is known as high-harmonic spectroscopy (HHS)
On account of the strong nonlinearity of the ionization process in HHG, HHS of molecules can sensitively and selectively probe the highest occupied molecular orbitals (HOMOs), which are of prime importance for understanding chemical reactions
Summary
High-harmonic generation (HHG) is a result of interactions between a freed electron and its parent ion, occurring under strong laser fields [1]. Since HHG contains information about the electron-ion interaction, one can retrieve the electronic state of the generating medium from the amplitudes and phases of the high-harmonic spectra. This technique is known as high-harmonic spectroscopy (HHS).
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