68 research outputs found
Distortion dependent intersystem crossing:a femtosecond time-resolved photoelectron spectroscopy study of benzene, toluene, and p-xylene
The competition between ultrafast intersystem crossing and internal conversion in benzene, toluene, and p-xylene is investigated with time-resolved photoelectron spectroscopy and quantum chemical calculations. By exciting to S2 out-of-plane symmetry breaking, distortions are activated at early times whereupon spin-forbidden intersystem crossing becomes (partly) allowed. Natural bond orbital analysis suggests that the pinnacle carbon atoms distorting from the aromatic plane change hybridization between the planar Franck-Condon geometry and the deformed (boat-shaped) S2 equilibrium geometry. The effect is observed to increase in the presence of methyl-groups on the pinnacle carbon-atoms, where largest extents of σ and π orbital-mixing are observed. This is fully consistent with the time-resolved spectroscopy data: Toluene and p-xylene show evidence for ultrafast triplet formation competing with internal conversion, while benzene appears to only decay via internal conversion within the singlet manifold. For toluene and p-xylene, internal conversion to S1 and intersystem crossing to T3 occur within the time-resolution of our instrument. The receiver triplet state (T3) is found to undergo internal conversion in the triplet manifold within ≈100–150 fs (toluene) or ≈180–200 fs (p-xylene) as demonstrated by matching rise and decay components of upper and lower triplet states. Overall, the effect of methylation is found to both increase the intersystem crossing probability and direct the molecular axis of the excited state dynamics
Perspective: Preservation of coherence in photophysical processes
Coherence is one of the most important phenomena in ultrafast sciences. We give our perspective on the terminology, observation, and preservation of coherence in photophysical processes with some glimpses to the past and some looking-head to what may pave the way for scaling one of the last bastions in ultrafast science, namely, that of mode specific chemistry where it will be possible to break any specific bond by tailoring the pulse, an accomplishment that obviously would be the dream of any chemist
The role of novel Rydberg-valence behaviour in the non-adiabatic dynamics of tertiary aliphatic amines
Time-resolved photoelectron imaging was used to study non-adiabatic relaxation dynamics in N,N-dimethylisopropylamine, N,N-dimethylpropylamine and N-methylpyrrolidine following excitation at 200 nm.</p
Tuning and Tracking of Coherent Shear Waves in Molecular Films
We have determined the time-dependent
displacement fields in molecular sub-micrometer thin films as response
to femtosecond and picosecond laser pulse heating by time-resolved
X-ray diffraction. This method allows a direct absolute determination
of the molecular displacements induced by electron–phonon interactions,
which are crucial for, for example, charge transport in organic electronic
devices. We demonstrate that two different modes of coherent shear
motion can be photoexcited in a thin film of organic molecules by
careful tuning of the laser penetration depth relative to the thickness
of the film. The measured response of the organic film to impulse
heating is explained by a thermoelastic model and reveals the spatially
resolved displacement in the film. Thereby, information about the
profile of the energy deposition in the film as well as about the
mechanical interaction with the substrate material is obtained
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