Chemical Dynamics

Research Interests

We specialize on developing exact and approximate quantum dynamics methods to investigate a broad range of chemical processes like excited-state proton transfer and dissociation and gas-phase and gas-surface reactive scattering. A list of processes we are interested in a list of methods we develop and apply can be found below.

Chemical dynamics

Excited-state electron and proton transfer
Ionization dynamics of molecules and clusters
Time-resolved XUV and X-ray spectroscopies
Attosecond physics and chemistry
Linear and non-linear THz spectroscopy
State-resolved reactive scattering
Surface reactions
Proton-coupled electron transfer

Method development of quantum and semi-classical molecular dynamics approaches

Multi Configuration Time-Dependent Hartree (MCTDH) and multi-layer MCTDH (ml-MCTDH)
Ring-Polymer Molecular Dynamics (RPMD)
Centroid Molecular Dynamics (CMD)
Mixed quantum/classical approaches

Research Highlights

Electronic coherence, nuclear motion and attochemistry. With the dawn of attosecond pulses, it is now possible to create coherent superpositions of excited electronic states of a photo-ionized molecule. However, typical simulations of the subsequent dynamics focus on the electronic motion and neglect the nuclear motion, even up to tens of femtosecons propagation time. This led to the prediction of long-lived electronic coherences. We adopted a full-dimensional quantum dynamics framework to study the influence of nuclear motion on electronic coherence. We found that nuclear motion typically leads to loss of coherence within 2-3 fs. In large organic molecules this effect is caused by motion along several low-frequency vibrational modes that show different gradients in the different electronic states. We furthermore investigated the influence of non-adiabatic coupling on the electronic coherence. We found that for cases where a conical intersection is close to the Franck-Condon point, the coherence can be partially preserved. Additionally, we showed that by introducing a relative phase between the two electronic states it is possible to steer the nuclear wavepacket allowing for attochemistry.

Details will be available in [PRA 95, 033425 (2017)] and soon in an additional publication.

 

XUV induced dissociation dynamics of the benzene cation. Benzene is the building block of polycyclic aromatic hydrocarbons (PAH), which are believed are considered precursors for the formation of complex biological molecules in the interstellar medium. We assessed the possibility of utilizing a Koopmans' theorem based approach to obtain electronic structure information in combination with the fewest switches surface hopping approach to study the XUV induced photodissociation of medium sized to large molecules. Good performance for the short-time nonadiabatic dynamics is found. Nonetheless, this work also highlights the challenges in XUV induced photochemistry as the adopted computationally efficient electronic structure method overestimates the dissociation barriers compare to more accurate, yet more expensive, methods.   Details will be available in a publication soon.

 

 

Electron hole density evolution in CO2 after creation of a superposition of electron hole state by ionization with an XUV laser. The electron hole evolves in a period of 110 fs and its dynamics is coupled to nuclear displacements through non-adiabatic coupling effects.

For details see [PRL 113, 113003 (2014)]

 

Electron hole density in a protonated water cluster consisting of 21 water molecules. D0 is the ground electronic state of the ion whereas D62 corresponds to a highly excited valence ionic state. Valence holes relax via non-adiabatic effects with 100 fs after ionization. We propose that this relaxation can be followed by time-resolved x-ray absorption spectroscopy.

Further details can be found in [Farad. Disc. 171, 457-470 (2014)]