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“…The assignment of the spectrum and the qualitative picture of the dynamics are made in analogy to the closely related acrolein. 58 We pump the S 2 state with 228 nm pulses of sub-60 fs duration. The transient spectra are measured with the three continuum ranges I-III ( Fig.…”
Complex multi-stage relaxation and reaction pathways after the optical excitation of molecules makes the disentanglement of the underlying mechanisms challenging. We present four examples that a new transient spectrometer with excitation fully tunable from the deep UV to the IR and 225 to 1700 nm probing allows for an analysis with greatly reduced ambiguity. The temporal resolution of about 50 fs allows us to resolve all relevant processes. For each example there is a new twist in the sequence of relaxation steps that had previously been overlooked. In malachite green it appears that the importance of the phenyl twisting has been overemphasized and rather a charge transfer state should be considered. In TINUVIN-P the predicted twisting as the driving motion for the ultrafast IC is confirmed and leads to a resolution of the earlier puzzle that the sub-5 ps regime shows kinetics deviating from a pure cooling process despite the sub-ps proton transfer cycle. For the bond cleavage of Ph 2 CH-Cl and Ph 2 CH-Br the degree of electron transfer within the radical pair can now be determined quantitatively and leads to a profound understanding of the long term cation yield. For the first time coherent wavepacket motion in the photoproducts is reported. Last but not least the measurement of the GSB recovery in the deep UV allows for the surprising result, that even after S 2 excitation of cyclopentenones the triplet states are reached with near unity probability within a few picoseconds.
“…The assignment of the spectrum and the qualitative picture of the dynamics are made in analogy to the closely related acrolein. 58 We pump the S 2 state with 228 nm pulses of sub-60 fs duration. The transient spectra are measured with the three continuum ranges I-III ( Fig.…”
Complex multi-stage relaxation and reaction pathways after the optical excitation of molecules makes the disentanglement of the underlying mechanisms challenging. We present four examples that a new transient spectrometer with excitation fully tunable from the deep UV to the IR and 225 to 1700 nm probing allows for an analysis with greatly reduced ambiguity. The temporal resolution of about 50 fs allows us to resolve all relevant processes. For each example there is a new twist in the sequence of relaxation steps that had previously been overlooked. In malachite green it appears that the importance of the phenyl twisting has been overemphasized and rather a charge transfer state should be considered. In TINUVIN-P the predicted twisting as the driving motion for the ultrafast IC is confirmed and leads to a resolution of the earlier puzzle that the sub-5 ps regime shows kinetics deviating from a pure cooling process despite the sub-ps proton transfer cycle. For the bond cleavage of Ph 2 CH-Cl and Ph 2 CH-Br the degree of electron transfer within the radical pair can now be determined quantitatively and leads to a profound understanding of the long term cation yield. For the first time coherent wavepacket motion in the photoproducts is reported. Last but not least the measurement of the GSB recovery in the deep UV allows for the surprising result, that even after S 2 excitation of cyclopentenones the triplet states are reached with near unity probability within a few picoseconds.
“…For example, the dynamics in butadiene (CH 2 =CH-CH=CH 2 ) takes place within 100 fs after light absorption [1]. However, there exist examples where this is not the case as, e.g., for α,β-enones [2,3]. In acrolein (CH 2 =CH-CH=O) a CH 2 -group of butadiene is replaced by an oxygen and triplet state formation can be observed although both butadiene and acrolein dynamics are governed by ethylene-type CoIns which are localized only at one side of the molecule [2].…”
Section: The Role Of Triplet State Dynamicsmentioning
confidence: 99%
“…However, there exist examples where this is not the case as, e.g., for α,β-enones [2,3]. In acrolein (CH 2 =CH-CH=O) a CH 2 -group of butadiene is replaced by an oxygen and triplet state formation can be observed although both butadiene and acrolein dynamics are governed by ethylene-type CoIns which are localized only at one side of the molecule [2]. So the question arises as to why such a small change in the molecular structure causes completely different dynamics.…”
Section: The Role Of Triplet State Dynamicsmentioning
Abstract. The origin of ultrafast intersystem crossing and its competitiveness with singlet pathways was studied in cyclic α,β-enones by transient absorption, time-resolved photoelectron spectroscopy and ab initio calculations.
“…All four states are coupled to each other by CoIns and consecutive state jumps back to the ground state are observed in our trajectory simulations as well as under experimental conditions. 15 The time evolution for the first 500 fs of P I is shown in Fig. 5.…”
Section: Transitionmentioning
confidence: 99%
“…The main reaction mechanism is a fast internal conversion taking the system back into electronic ground state. 15 The conjugated π-system formed by the C= =C and the C= =O group is involved in the non-adiabatic couplings between the electronic states.…”
Femtosecond Stimulated Raman Spectroscopy (FSRS) signals that monitor the excited state conical intersections dynamics of acrolein are simulated. An effective time dependent Hamiltonian for two C—H vibrational marker bands is constructed on the fly using a local mode expansion combined with a semi-classical surface hopping simulation protocol. The signals are obtained by a direct forward and backward propagation of the vibrational wave function on a numerical grid. Earlier work is extended to fully incorporate the anharmonicities and intermode couplings.
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