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Using a X-ray free-electron laser to probe photo-isomerisation

29 June 2012


Jonathan G. Underwood & co-authors

Transient X-Ray Fragmentation: Probing a Prototypical Photoinduced Ring Opening

Phys. Rev. Lett. 108, 253006 (2012)


An international team of scientists including UCL's Dr Jonathan Underwood report the first study of UV-induced photoisomerisation probed via core ionisation by the femtosecond LCLS x-ray free-electron laser at SLAC in Stanford, US. They investigated x-ray ionization and fragmentation of the cyclohexadiene-hexatriene system at 850 eV during the ring opening. The key finding is that the ion-fragmentation patterns evolve over a picosecond, reflecting a change in the state of excitation and the molecular geometry: the average kinetic energy per ion fragment and H+-ion count increase as the ring opens and the molecule elongates.

This result opens the door to new opportunities for ultrafast x-ray probing of molecular photophysics with femtosecond x-ray probe free-electron laser light sources.

Average kinetic energy per fragment as a function of time delay after the UV excitation in UV x ray (blue, left axis) and UV IR (red, right axis) CHD ring-opening experiments. The inset shows the electronic states of the CHDHT pair.

Image:

Average kinetic energy per fragment as a function of time delay after the UV excitation in UV x ray (blue, left axis) and UV IR (red, right axis) CHD ring-opening experiments. The inset shows the electronic states of the CHDHT pair