Theoretical studies of inelastic atomic collisions in a two-state model problem

A two-state scattering problem in which two non-crossing Morse curves are coupled by an exponential potential is discussed theoretically in both the diabatic and adiabatic approximations. Inelastic cross sections are estimated by various approximate analytical formulas, which are expressed in terms of the distorted wave matrix elements. The Landau (steepest descent) method is applied to estimate the distorted wave matrix element. The previously proposed separable potential approximation in the adiabatic method is found to be best among others by comparing with the exact numerical results. Transition probability as a function of l (angular momentum of relative motion) is well reproduced by this approximation. A glory effect in the velocity dependence of the cross section is found in the low energy region, and the adiabatic approximation reproduces this undulation phenomenon well.     

Low-energy inelastic atomic collisions of magnesium and hydrogen

The available quantum calculations of inelastic cross sections were analyzed for processes in collisions Mg + H and Mg⁺ + H^–. The cross sections with large values were obtained with high accuracy. These processes are of particular interest for astrophysics.     

Delta electrons: An atomic clock for deep inelastic collisions

We calculate the δ-electron distribution resulting from heavy ion collisions with projectile energies above the Coulomb barrier. It is shown that the life time (Δτ?10^?21s) of superheavy composite systems causes pronounced oscillations in the electron spectrum. The width of the oscillations is found to be ΔE=h/Δτ. This effect can be used to measure nuclear sticking times quite accurately.     

Multiscaling in inelastic collisions

We study relaxation properties of two-body collisions on the mean-field level. We show that this process exhibits multiscaling asymptotic behavior as the underlying distribution is characterized by an infinite set of nontrivial exponents. These nonequilibrium relaxation characteristics are found to be closely related to the steady state properties of the system.     

Laser-Assisted particle-atom inelastic collisions. Role of the field polarization

Summary A theoretical treatment, of first order in the collision dynamics, is presented to analyse the role of electric polarization in offresonance laser-assisted atomic collisions. General expressions are presented for evaluating the modified spectrum and wave functions for anyn level of hydrogenic atoms in the presence of a laser, taken to be linearly and circularly polarized. Specific calculations are carried out for excitation of hydrogen atoms to the leveln=2 by electron impact. The two polarizations are found to yield large differences i) in the atomic-spectrum modifications, ii) in the structure of the cross-sections and iii) in the numerical results. In particular, only for linear polarization, the distribution in energy of the scattered electrons at a fixed scattering angle has the structure of a series of equally spaced lines of different height (the spacing being equal to the laser photon energy ℏw and the height of the line accounting for the number of final electrons with a given energy). For circular polarization no such a regular pattern is predicted. Since, among laser-assisted particle-atom collisions, at present energy gain-loss spectra of scattered electrons are most easily observed, it is hoped that the reported results may serve as a stimulus for new observations in this new class of atomic collisions. The theory to treat the multiphoton resonance case is outlined too. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Quantum state control via trap-induced shape resonance in ultracold atomic collisions

We investigate controlled collisions between trapped but separated ultracold atoms. The interaction between atoms is treated self-consistently using an energy-dependent delta-function pseudopotential model, whose validity we establish. At a critical separation, a "trap-induced shape resonance" between molecular bound states and a vibrational eigenstate of the trap can occur. This resonance leads to an avoided crossing in the eigenspectrum as a function of separation. We investigate how this new resonance can be employed for quantum control.     

Ultracold inelastic collisions in two dimensions

We show that cross sections for inelastic collisions of ultracold atoms or molecules confined by a harmonic potential have the same energy dependence as in pure 2D geometry. This indicates that chemical reactions and inelastic collisions may be suppressed in an ultracold gas under strong confinement in one dimension. We present a numerical proof of the threshold collision laws in 2D. Our results indicate that inelastic collisions in weak electromagnetic fields may be controlled by varying the orientation of the external field axis with respect to the plane of confinement.     

Spin effects in inelastic electron-atom collisions

Recent progress of experimental investigations that show explicitly spin-dependent effects is reported for inelastic electron-atom scattering. In particular the combined effect of exchange scattering and target coupling is discussed in more detail. The experimental investigation of this ‘target-coupling effect’ is a powerful method to study the influence of exchange scattering directly. The experiments that are reviewed are basically target and electron spin-polarization measurements and the determination of the angular momentum state of the atom after scattering.     

Angular-momentum coherence in heavy-ion deep inelastic collisions

It is shown that cross sections describing deep inelastic collisions between complex nuclei can neither be desribed as a coherent nor as an incoherent superposition of partial-wave amplitudes. The number of interfering partial waves increases with the masses of the interacting nuclei and decreases with the interaction time.     

The third particle in deep inelastic collisions

Angular correlations between charged reaction products have been measured for the reaction¹⁴N+²⁷A1 at 70 and 100 MeV. Light particle evaporation from the heavy recoil is shown to be the dominant process. In addition, however fast alphas are observed for all reaction channels. From the three-body kinematics we conclude that these alphas are emitted from the contact zone between the two heavy ions. A comparison of the results forE _Lab=70 and 100 MeV excludes an explanation of this process by the recently suggested “Piston” or “hot-spot” models.     

Collective effects in atomic collisions

As a first step towards a collective treatment of charge flow in atomic collisions, we constructab initio potential energy surfaces as a function of the internuclear distance and the charge asymmetry between the two atomic species. To this end, the charge asymmetry off its stability value for a given nuclear separation is imposed upon the system by a suitable constraint within a two-centre Hartree-Fock calculation. Energy surfaces are presented for the systems LiH, HF, LiF, and CO. This representation offers a conceptual framework for visualising ionic or covalent molecular states and trajectories describing charge-changing collisions.     

A classical description of deep inelastic collisions

A classical friction model is applied to describe deep inelastic collisions between heavy ions. With only a very few parameters chosen once and for all, a quantitative fit to the existing fusion data as well as the different features of deep inelastic scattering are obtained.     

Competing scaling laws in deep inelastic hadron collisions

We have investigated the electro-fission of uranium in the energy range from 15 to 40 MeV with electrons and positrons. Bumps in the cross-section ratio σ^?/σ⁺ are explained as E2 admixtures after the onset of higher-chance fission.     

Physics of atomic collisions in retrospect

The classic work by Mott and Massey, in which the scope of the physics of atomic collisions was defined, was published about 65 years ago. Since then, this field has undergone considerable development. In fact, all the theoretical methods named by Mott and Massey have been implemented to some extent. As for experiment, the measurements performed, which are differential with respect to several parameters, have provided for reliable testing of the mechanisms proposed. The physics of atomic collisions has been developed to the point that we can look back on the road taken and discover many achievements which have promoted its development. Progress in science is usually associated with highly concentrated efforts on the part of a critical number of investigators to solve a specific problem, which is widely regarded as being of great importance. Such a “breakthrough” is usually followed by rapid development of the field. In this respect, the physics of atomic collisions is no exception. It has known periods of highly concentrated efforts aimed at solving specific problems and breakthroughs followed by rapid development and subsequent periods of stagnation. The cycles have repeated: a new area for concentrated efforts is discovered, a breakthrough occurs, and a new concept is established. Some of these cycles are analyzed from the standpoint of their significance to atomic physics as a whole. Zh. Tekh. Fiz. 69, 22–26 (September 1999)