Simona Scheit

On the interatomic Coulombic decay in the Ne dimer

The interatomic Coulombic decay (ICD) in the Ne dimer is discussed in view of the recent experimental results. The ICD electron spectrum and the kinetic energy release of the Ne+ fragments resulting after Coulomb explosion of Ne2 (2+) are computed and compared to the measured ones. A very good agreement is found, confirming the dynamics predicted for this decay mechanism. The effect of the temperature on the electron spectrum is briefly investigated.

Time-dependent interplay between electron emission and fragmentation in the interatomic Coulombic decay

The electronic decay of the Ne2+ cation by electron emission is studied. This interatomic Coulombic decay (ICD) follows inner valence ionization of the neon dimer and the decay rate depends strongly on the internuclear distance. The time-dependent theory of wave packet propagation is applied allowing to follow the evolution of the decay process in time. The impact of nuclear dynamics on the decay spectrum is investigated. Among others, the spectrum corresponding to the decay of the 2 2Σu+ electronic state of the Ne2+ cation is calculated at different times. Its characteristics are found to be influenced considerably by the nuclear motion. A pronounced oscillatory structure appears: Its origin is explained and related to the interatomic nature of the ICD process. Particularly enlightening for the understanding of the ICD process is the analysis of the total energy distribution in the final system resulting after the fragmentation of the Ne22+ dication, produced by the ICD of Ne2+.

Interatomic Coulombic decay in a heteroatomic rare gas cluster

Interatomic decay in a heteroatomic rare gas cluster (NeAr) is studied in detail using ab initio electronic structure description and nuclear dynamics simulations. Decay widths of all possible interatomic decay processes are calculated by the recently developed method based on Greens function formalism. Kinetic energy spectra of the electrons emitted in the course of interatomic Coulombic decay (ICD) are simulated for a series of initial vibrational states of the neutral cluster. The effect of the nuclear dynamics on the ICD electron spectra is discussed.

Controlled Dynamics at an Avoided Crossing Interpreted in Terms of Dynamically Fluctuating Potential Energy Curves

The nonadiabatic nuclear wavepacket dynamics on the coupled two lowest (1)Σ(+) states of the LiF molecule under the action of a control pulse is investigated. The control is achieved by a modulation of the characteristics of the potential energy curves using an infrared field with a cycle duration comparable to the time scale of nuclear dynamics. The transition of population between the states is interpreted on the basis of the coupled nuclear wavepacket dynamics on the effective potential curves, which are transformed from the adiabatic potential curves with use of a diabatic representation that diagonalizes the dipole-moment matrix of the relevant electronic states. The basic feature of the transition dynamics is characterized in terms of the notion of the collision between the dynamical crossing point and nuclear wavepackets running on such modulated potential curves, and the transition amplitude is mainly dominated by the off-diagonal matrix element of the time-independent electronic Hamiltonian in the present diabatic representation. The importance of the geometry dependence of the intrinsic dipole moments as well as of the diabatic coupling potential is illustrated both theoretically and numerically.

Interatomic Coulombic decay and its dynamics in NeAr following K-LL Auger transition in the Ne atom

We analyze in detail the accessible relaxation pathways via electron emission of the Ne2+Ar states populated via the K-LL Auger decay of Ne+(1s−1)Ar. In particular, we concentrate on the “direct” interatomic Coulombic decay (ICD) of the Ne2+(2s−12p−1)Ar weakly bound doubly ionized states into the manifold of the Ne2+(2p−2)–Ar+(3p−1) repulsive triply ionized ones. To carry out the present study the potential energy curves of the NeAr ground state, the core ionized state Ne+(1s−1)Ar, the relevant dicationic and tricationic states, and the corresponding ICD transition rates have been computed using accurate ab initio methods and basis sets. The total and partial ICD electron spectra are computed within the framework of the time-dependent theory of wave packet propagation. Thereby, the impact of nuclear dynamics accompanying the electronic decay on the computed ICD-electron spectra is investigated in detail.

Non-Hermitian quantum mechanics: Wave packet propagation on autoionizing potential energy surfaces

The correspondence between the time-dependent and time-independent molecular dynamic formalisms is shown for autoionizing processes. We demonstrate that the definition of the inner product in non-Hermitian quantum mechanics plays a key role in the proof. When the final state of the process is dissociative, it is technically favorable to introduce a complex absorbing potential into the calculations. The conditions which this potential should fulfill are briefly discussed. An illustrative numerical example is presented involving three potential energy surfaces.

Communication: Induced photoemission from nonadiabatic dynamics assisted by dynamical Stark effect

Through nonadiabatic interaction due to electron transfer as that in alkali halides, vibrational dynamics on the ionic potential energy surface (large dipole moment) is coupled to that on the covalent surface (small dipole moment). Thus, population transfer between the states should cause long-range electron jump between two remote sites, which thereby leads to a sudden change of the large molecular dipole moment. Therefore, by making repeated use of the dynamical Stark effect, one may expect emission of photons from it. We show with coupled quantum wavepacket dynamics calculation that such photoemission can indeed occur and can be controlled by an external field. The present photoemission can offer an alternative scheme to study femtosecond and subfemtosecond vibrational and electronic dynamics and may serve as a unique optical source.

Induced photoemission from driven nonadiabatic dynamics in an avoided crossing system

When vibrational dynamics on an ionic state (large dipole moment) is coupled to that on a neutral state (small dipole moment) such as at an avoided crossing in the alkali halide system, the population transfer between the states cause oscillation of the molecular dipole, leading to dipole emission. Such dynamics may be driven by an external field. We study how the coupled wavepacket dynamics is affected by the parameters (intensity, frequency) of the driving field with the aim of making use of the photoemission as an alternative detection scheme of femtosecond and subfemtosecond vibrational and electronic dynamics or as a characteristic optical source.

Control scheme of nonadiabatic transitions with the dynamical shift of potential curve crossing.

We investigate how the nuclear dynamics at an avoided crossing is affected and can be controlled by the introduction of a laser field whose cycle is comparable to the time-scale of the nuclear dynamics. By introducing the concepts of light-induced effective potential energy curves and dynamical avoided crossing, we describe the laser controlled nuclear dynamics and present basic control scenarios, giving a detailed explanation of the underlying dynamical mechanisms. The scenarios presented allow for examples to understand from a different perspective the results of dynamic Stark control experiments. The proposed interpretation is applied to the laser-controlled nonadiabatic dynamics between the two lowest (1)Σ(+) states of LiF, where the usefulness of the concepts developed is elucidated.

Few-femtosecond passage of conical intersections in the benzene cation

Observing the crucial first few femtoseconds of photochemical reactions requires tools typically not available in the femtochemistry toolkit. Such dynamics are now within reach with the instruments provided by attosecond science. Here, we apply experimental and theoretical methods to assess the ultrafast nonadiabatic vibronic processes in a prototypical complex system—the excited benzene cation. We use few-femtosecond duration extreme ultraviolet and visible/near-infrared laser pulses to prepare and probe excited cationic states and observe two relaxation timescales of 11 ± 3 fs and 110 ± 20 fs. These are interpreted in terms of population transfer via two sequential conical intersections. The experimental results are quantitatively compared with state-of-the-art multi-configuration time-dependent Hartree calculations showing convincing agreement in the timescales. By characterising one of the fastest internal conversion processes studied to date, we enter an extreme regime of ultrafast molecular dynamics, paving the way to tracking and controlling purely electronic dynamics in complex molecules.Attosecond science is beginning to provide the tools to study the previously unattainable crucial first few femtoseconds of photochemical reactions. Here, the authors investigate extremely rapid population transfer via conical intersections in the excited benzene cation, both by experiment and computation.