2 research outputs found
Observation of Ultrafast Charge Migration in an Amino Acid
We present the first direct measurement of ultrafast
charge migration
in a biomolecular building block – the amino acid phenylalanine.
Using an extreme ultraviolet pulse of 1.5 fs duration to ionize molecules
isolated in the gas phase, the location of the resulting hole was
probed by a 6 fs visible/near-infrared pulse. By measuring the yield
of a doubly charged ion as a function of the delay between the two
pulses, the positive hole was observed to migrate to one end of the
cation within 30 fs. This process is likely to originate from even
faster coherent charge oscillations in the molecule being dephased
by bond stretching which eventually localizes the final position of
the charge. This demonstration offers a clear template for observing
and controlling this phenomenon in the future
Few-Femtosecond C<sub>2</sub>H<sub>4</sub><sup>+</sup> Internal Relaxation Dynamics Accessed by Selective Excitation
Dissociation
of the ethylene cation is a prototypical multistep
pathway in which the exact mechanisms leading to internal energy conversions
are not fully known. For example, it is still unclear how the energy
is exactly redistributed among the internal modes and which step is
rate-determining. Here we use few-femtosecond extreme-ultraviolet
pulses of tunable energy to excite a different superposition of the
four lowest states of C2H4+ and probe
the subsequent fast relaxation with a short infrared pulse. Our results
demonstrate that the infrared pulse photoexcites the cationic ground
state (GS) to higher excited states, producing a hot GS upon relaxation,
which enhances the fragmentation yield. As the photoexcitation probability
of the GS strongly depends on the molecular geometry, the probing
by the IR pulse provides information about the ultrafast excited-state
dynamics and the type of conical intersection (planar or twisted)
involved in the first 20 fs of the nonradiative relaxation