We present the semiclassical laser field induced surface hopping method for the simulation and control of coupled electron-nuclear dynamics in complex molecular systems including all degrees of freedom. Our approach is based on the Wigner representation of quantum mechanics. The combination of the molecular dynamics "on the fly" employing quantum initial conditions with the surface hopping procedure allows for the treatment of the electronic transitions induced by the laser field. Our semiclassical approach reproduced accurately exact quantum dynamics in a two electronic state model system. We demonstrate the scope of our method on the example of the optimal pump-dump control of the trans-cis isomerization of a prototypical Schiff base molecular switch. Our results show that selective photochemistry can be achieved by shaped laser pulses which open new dynamical pathways by suppressing the isomerization through the conical intersections between electronic states.
We present the extension of our field-induced surface hopping method for the description of the photoionization process and the simulation of time-resolved photoelectron spectra (TRPES). This is based on the combination of nonadiabatic molecular dynamics "on the fly" in the framework of TDDFT generalized for open shell systems under the influence of laser fields with the approximate quantum mechanical description of the photoionization process. Since arbitrary pulse shapes can be employed, this method can be also combined with the optimal control theory in order to steer the photoionization or to shape the outgoing electronic wavepackets. We illustrate our method for the simulation of TRPES on the prototype system of Ag(3), which involves excitation from the equilibrium triangular geometry, as well as excitation from the linear transition state, where in both cases nonadiabatic relaxation takes place in a complex manifold of electronic states. Our approach represents a generally applicable method for the prediction of time-resolved photoelectron spectra and their analysis in systems with complex electronic structure as well as many nuclear degrees freedom. This theoretical development should serve to stimulate new ultrafast experiments.
We present a general mechanism for successful discrimination of spectroscopically indistinguishable biochromophores by shaped light. For this purpose we use nonadiabatic dynamics in excited electronic states in the frame of the field-induced surface hopping method driven by the experimentally shaped laser fields. Our findings show that optimal laser fields drive low-frequency vibrational modes localized in the side chains of two biochromophores, thus selecting the parts of their potential energy surfaces characterized by different transition dipole moments leading to different ionization probabilities. The presented mechanism leads to selective fluorescence depletion which serves as a discrimination signal. Our findings offer a promising perspective for using optimally shaped laser pulses in bioanalytical applications by increasing the selectivity beyond the current capability.
We present photoluminescence spectra and excited state decay rates of a series of diamondoids, which represent molecular structural analogues to hydrogen-passivated bulk diamond. Specific isomers of the five smallest diamondoids (adamantane-pentamantane) have been brought into the gas phase and irradiated with synchrotron radiation. All investigated compounds show intrinsic photoluminescence in the ultraviolet spectral region. The emission spectra exhibit pronounced vibrational fine structure which is analyzed using quantum chemical calculations. We show that the geometrical relaxation of the first excited state of adamantane, exhibiting Rydberg character, leads to the loss of T d symmetry. The luminescence of adamantane is attributed to a transition from the delocalized first excited state into different vibrational modes of the electronic ground state. Similar geometrical changes of the excited state structure have also been identified in the other investigated diamondoids. The excited state decay rates show a clear dependence on the size of the diamondoid, but are independent of the particle geometry, further indicating a loss of particle symmetry upon electronic excitation.
We present the simulation of time-resolved photoelectron spectra of Ag(3) involving excitation from the linear transition state, where nonadiabatic relaxation takes place in a complex manifold of electronic states. Thus, we address ultrafast processes reachable by negative ion-to neutral-to positive ion (NeNePo) spectroscopy starting from the linear Ag anionic species. For this purpose we use our newly developed field-induced surface hopping method (FISH) augmented for the description of photoionization processes. Furthermore we employ our method for nonadiabatic molecular dynamics "on the fly" in the framework of time-dependent density functional theory generalized for open shell systems. Our presented approach is generally applicable for the prediction of time-resolved photoelectron spectra and their analysis in systems with complex electronic structure as well as many nuclear degrees freedom. This theoretical development should serve to stimulate new ultrafast experiments.
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