Topics in current chemistry

Electronic and vibronic excitations as well as fragmentation mechanisms in high energy ion ( ${\mathrm{H}}^{+}$, ${\mathrm{C}}^{+}$, ${\mathrm{Ar}}^{+}$) fullerene collisions are investigated within a fully microscopic approach, called nonadiabatic quantum molecular dynamics. The total kinetic energy loss of the projectile depends dramatically on ion mass, but, surprisingly, does not depend on the impact velocity for all ions in a certain range. This is in striking contrast to the predictions of the ``stopping power'' concept of solids, but explains apparently contradicting experimental observations. Signatures for nonstatistical fragmentation mechanisms are predicted.

Excitation and fragmentation mechanisms in ion-fullerene collisions.

A mixed quantum-classical approach to simulate the coupled dynamics of electrons and nuclei in nanoscale molecular systems is presented. The method relies on a second order expansion of the Lagrangian in time-dependent density functional theory (TDDFT) around a suitable reference density. We show that the inclusion of the second order term renders the method a self-consistent scheme and improves the calculated optical spectra of molecules by a proper treatment of the coupled response. In the application to ion-fullerene collisions, the inclusion of self-consistency is found to be crucial for a correct description of the charge transfer between projectile and target. For a model of the photoreceptor in retinal proteins, nonadiabatic molecular dynamics simulations are performed and reveal problems of TDDFT in the prediction of intra-molecular charge transfer excitations.

Importance of electronic self-consistency in the TDDFT based treatment of nonadiabatic molecular dynamics

We present a static classical over-the-barrier model (OBM) for electron transfer between two isolated, infinitely conducting spheres with arbitrary and different electrical charges. This model is shown to be very useful for first estimates of single- and multiple-electron transfer cross sections in cluster-cluster collisions when the collision velocities are significantly lower than the typical target electron velocities. For faster collisions, more advanced models such as the dynamical OBM, or the time-dependent local density approximation (TDLDA) or the solutions of their semiclassical counterparts---the Vlasov equations have to be used. The latter two methods clearly provide the most detailed information on the electronic response, but they are also computationally very demanding and have, so far, only been used for collisions involving one cluster (and an atomic ion). We compare our static OBM results (in the limit in which one of the sphere radii approaches zero) with TDLDA and Vlasov calculations of cluster charging in ${\mathrm{Ar}}^{8+}\ensuremath{-}{\mathrm{Na}}_{40}$ collisions at different velocities to demonstrate that the present static OBM is valid at sufficiently low velocities. The static OBM is then used in a comparison with experimental target charge state distributions in ${\mathrm{C}}_{60}^{q+}\ensuremath{-}{\mathrm{C}}_{60}$ and ${\mathrm{C}}^{q+}\ensuremath{-}{\mathrm{C}}_{60}$ collisions at $0.01\sqrt{q}$ and $0.06\sqrt{q}{v}_{0},$ respectively. Calculated electronic excitation of the projectile after two-electron transfer in ${\mathrm{C}}_{60}^{4+}\ensuremath{-}{\mathrm{C}}_{60}$ collisions readily explains the recently observed suppression of the transfer ionization channel in this reaction. Finally, we model the total projectile electron loss and dissociation cross section in highly protonated Lysozyme-oxygen $(\mathrm{Lys}\ensuremath{-}{\mathrm{H}}_{9}^{9+}\ensuremath{-}{\mathrm{O}}_{2})$ collisions and make comparisons with recent experimental results at $0.01{v}_{0}.$

Static over-the-barrier model for electron transfer between metallic spherical objects

Scattering of a proton with the Li4 cluster: Non-adiabatic molecular dynamics description based on time-dependent density-functional theory

Charge transfer in collisions of Na_n^+ cluster ions with Cs atoms is investigated theoretically in the microscopic framework of non-adiabatic quantum molecular dynamics. The competing reaction channels and related processes affecting the charge transfer (electronic excitations, fragmentation, temperature) are described. Absolute charge transfer cross sections for Na_n^+(2.7 keV) + Cs --> Na_n + Cs^+ have been calculated in the size range 4 <= n <= 11 reproducing the size dependence of the experimental cross sections. The energy dependence of the cross section is predicted for n=4,7,9. An exotic charge transfer channel producing Cs^- is found to have a finite probability.

https://arxiv.org/pdf/physics/9712008.pdf

Charge Transfer in Cluster-Atom Collisions Studied with Non-Adiabatic Quantum Molecular Dynamics

Charge transfer and fragmentation in collisions of sodium cluster ions with caesium atoms have been investigated theoretically within a microscopic framework called nonadiabatic quantum molecular dynamics To illustrate the complexity of nonadiabatic cluster collisions, in particular the interplay between charge transfer and fragmentation, Na{sub 4}{sup +}(27 keV)+Cs collisions are studied in detail with special emphasis on methodical aspects It is shown that integral and exclusive charge transfer cross sections can be understood only if all types of fragmentation processes including statistical decay are taken into account The influence of the cluster structure (isomers, temperature, size) on measured and measurable cross sections is studied for different charge transfer channels as well as for fragmentation In particular, cross sections for the exotic formation of caesium anions in such collisions are predicted (c) 2000 The American Physical Society

Charge transfer and fragmentation in cluster-atom collisions

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Charge Transfer in Cluster-Atom Collisions Studied with Non-Adiabatic Quantum Molecular Dynamics

Charge transfer and fragmentation in cluster-atom collisions