High harmonic generation by halogen anions and noble gas atoms in a laser field

A comparative study of high harmonic generation (HHG) by atoms and ions with active p-electrons is carried out in the theoretical framework of the rescattering mechanism. The substate with m(l) = 0, i.e. zero orbital momentum projection along the electric vector of a linearly polarized laser wave, is found to give the major contribution to the HHG rate. Our calculations for HHG by an H atom in an excited 2p-state demonstrate that the rate for recombination into a final state with a different value of m(l) (= +/- 1), is higher for lower harmonic orders N, while for higher N (beyond the plateau domain) the difference vanishes. For species with closed electron shells, the m(l)-changing transitions are forbidden by the Pauli exclusion principle. We report absolute HHG rates for halogen ions and noble gas atoms at various intensities. These results demonstrate that the Coulomb binding potential of the atoms considerably enhances both the ionization and recombination steps in the rescattering process. However, the weak binding energy of the anions allows lower orders of HHG to be efficiently produced at relatively low intensities, from which we conclude that observation of HHG by an anion is experimentally feasible.

Correlation Effects in the Compton Profile of Silicon

Ab initio nonlocal pseudopotential variational quantum Monte Carlo techniques are used to compute the correlation effects on the valence momentum density and Compton profile of silicon. Our results for this case are in excellent agreement with the Lam-Platzman correction computed within the local density approximation. Within the approximations used, we rule out valence electron correlations as the dominant source of discrepancies between calculated and measured Compton profiles of silicon.

Counterbalancing forces in electromigration

In electromigration (EM) experiments on metallic wires, a flux of atoms can lead to motion of the centre of mass (COM) of the wire. Hence, it may be tempting to assume that the flow of current produces a net force on the wire as a whole. We point out, on the basis of known momentum-balance arguments, that the net force on a metallic wire due to a passing steady-state current is zero. This is possible, because in addition to EM driving forces, acting on scattering centres, there are counterbalancing forces, acting on the rest of the system. Drift of the COM in EM experiments occurs inevitably because the substrate keeps the crystal lattice of the wire fixed, while allowing diffusion of defects in the bulk of the wire. This drift is not evidence for a net force on the wire.

Time-dependent tight binding

Starting from a Lagrangian mean-field theory, a set of time-dependent tight-binding equations is derived to describe dynamically and self-consistently an interacting system of quantum electrons and classical nuclei. These equations conserve norm, total energy and total momentum. A comparison with other tight-binding models is made. A previous tight-binding result for forces on atoms in the presence of electrical current flow is generalized to the time-dependent domain and is taken beyond the limit of local charge neutrality.

On the origin of the forward peak and backward oscillations in the F + H2(v = 0) to HF(v' = 2) + H reaction

We present a semiclassical complex angular momentum (CAM) analysis of the forward scattering peak which occurs at a translational collision energy around 32 meV in the quantum mechanical calculations for the F + H2(v = 0, j = 0) ? HF(v' = 2, j' = 0) + H reaction on the Stark–Werner potential energy surface. The semiclassical CAM theory is modified to cover the forward and backward scattering angles. The peak is shown to result from constructive/destructive interference of the two Regge states associated with two resonances, one in the transition state region and the other in the exit channel van der Waals well. In addition, we demonstrate that the oscillations in the energy dependence of the backward differential cross section are caused by the interference between the direct backward scattering and the decay of the two resonance complexes returning to the backward direction after one full rotation.

Dynamical Equations For The Period Vectors In A Periodic System Under Constant External Stress

The purpose of this paper is to derive the dynamical equations for the period vectors of a periodic system under constant external stress. The explicit starting point is Newton’s second law applied to halves of the system. Later statistics over indistinguishable translated states and forces associated with transport of momentum are applied to the resulting dynamical equations. In the final expressions, the period vectors are driven by the imbalance between internal and external stresses. The internal stress is shown to have both full interaction and kinetic-energy terms.

Optical Thomson scatter from laser-ablated plumes

We have obtained density and temperature informations on an expanding KrF laser-ablated magnesium plume via optical Thomson scatter with a frequency doubled Nd:YAG laser. The electron temperature was found to decay with the expected Te t-1 dependence. However, we have found the electron density to have a time dependence ne t-4.95 which can be explained by strong recombination processes. We also observed atomic Raman satellites originating from transitions between the different angular momentum levels of the metastable 3P0 term in Mg I.