Symmetric resonant charge transfer in atomic collisions in the presence of a homogeneous constant magnetic field is investigated within the impact parameter method and the atomic two-state expansion. The novelties brought about by the presence of the magnetic field are discussed in detail. The most peculiar new feature is the appearance of a magnetic-field-dependent phase factor in the process wavefunction, which is responsible for severe reductions of the total cross section at moderately strong fields. Numerical evaluation of the transition probability and the total cross section is performed for the Rb + +Rb to Rb+Rb + reaction. Reduction of the cross section up to 43% are found at relative velocity nu =6.8*10 6 cm s -1 and magnetic field B=0.05 B 0 (B 0 =2.35*10 5 T being the atomic unit of magnetic strength). The magnetic field also enters the problem through a 'dressing' of the atomic states. With the values of the magnetic field strength considered, which affect the atomic energies only moderately, the dressing is found to have only secondary importance in determining the absolute values of the total cross section, which are mainly controlled by large impact parameters. Moreover the dressing is found to be important in modifying the oscillatory structure of the total cross section, which originates at small impact parameters.
Symmetric resonant charge transfer in atomic collisions in the presence of a homogeneous constant magnetic field is investigated within the impact parameter method and the atomic two-state expansion. The novelties brought about by the presence of the magnetic field are discussed in detail. The most peculiar new feature is the appearance of a magnetic-field-dependent phase factor in the process wavefunction, which is responsible for severe reductions of the total cross section at moderately strong fields. Numerical evaluation of the transition probability and the total cross section is performed for the Rb + +Rb to Rb+Rb + reaction. Reduction of the cross section up to 43% are found at relative velocity nu =6.810 6 cm s -1 and magnetic field B=0.05 B 0 (B 0 =2.3510 5 T being the atomic unit of magnetic strength). The magnetic field also enters the problem through a 'dressing' of the atomic states. With the values of the magnetic field strength considered, which affect the atomic energies only moderately, the dressing is found to have only secondary importance in determining the absolute values of the total cross section, which are mainly controlled by large impact parameters. Moreover the dressing is found to be important in modifying the oscillatory structure of the total cross section, which originates at small impact parameters.
Within the classical trajectory Monte Carlo (CTMC) model, we calculate electron transfer and ionization cross sections for singly charged ions colliding with Rydberg atoms in the presence of a laboratory-strength magnetic field of 4 tesla. A new method for generating a stationary microcanonical ensemble for a quasi-integrable initial-state Hamiltonian is presented. The calculated cross sections show signatures of electron capture and ionization mechanisms for the field-free case, e.g. multiple swaps and saddle-point electrons; their structure as well as their magnitude, however, are strongly modified by the presence of the magnetic field.
Alignment and orientation effects in collisions of helium with Rydberg atoms due to the presence of static electric and magnetic fields are predicted. Analytical expressions are obtained for the cross sections of the state-to-state transitions within the manifold with the same principal quantum number. For moderate field-induced inelasticity, the curves of the cross sections vs the fields intensity show modulations that are explained in terms of the phase differences accumulated by the wave functions of the states involved in the collision. Due to the presence of the magnetic field, transitions involving inversion of high magnetic quantum numbers are dramatically quenched. The possibility of observing the predicted effects is discussed. The reported analytical cross sections are expected to help in the understanding of the results.
We propose an efficient method of collisional transfer of transverse magnetic moment between different kinds of atoms using the spin-locking technique. Demonstrating experiments with a rotating or an oscillating rf field are carried out on a 85 Rb– 133 Cs vapor, and the transfer of a large amount of the transverse magnetic moment is observed when the amplitude H 1 of the rf field is comparable to the static magnetic field strength H 0 . The H 1 -dependence of the transfer, in the case of the oscillating rf field, is not simple, because of the Bloch-Siegert shift and associated resonance effects. The transfer of the transverse magnetic moment under the strong rf field is numerically analyzed with the Bloch equations for 85 Rb and 133 Cs coupled through spin-exchange collisions.
The effects of strong magnetic fields on thermal collisions in a vapor are reviewed. Semiclassical and quantum-mechanical symmetry properties of the relaxation matrix are established for resonant collisions between identical atoms and nonresonant collisions with a structureless partner. The variations with field strength of the transfer rates between Zeeman sublevels for ${R}^{\ensuremath{-}3}$ dipole-dipole interaction and ${R}^{\ensuremath{-}6}$ Van der Waals interaction are obtained with an exact semiclassical computation of the collision matrix. These are then compared with those predicted with an approximate formulation by means of the symmetrical correlation function for the potential.
The antihydrogen formation by charge exchange between cold antiprotons and Rydberg positronium Ps∗ is studied by using the classical trajectory Monte Carlo method. In the absence of external magnetic field the cross section scaled by the fourth power of the Ps∗ principal quantum number nPs shows a universal behavior as a function of the ratio kv between the velocity of the Ps center of mass and that of the positron in the classical circular orbit. At low velocity, below about ${k}_{v}\ensuremath{\simeq}0.2--0.3$, we show for Rydberg positronium that the cross section increases as 1/kv2 or, in an equivalent way, as 1/EPscm with EPscm being the Ps∗ center-of-mass energy. In this regime the distribution of the principal quantum number of the antihydrogen state is narrow and it shows a peak at about 2nPs while at higher kv values a broad distribution of antihydrogen states is produced. The study of the collision process in the presence of moderate magnetic field (0.5--2 T) shows that there is an experimentally interesting region of kv with the cross section slightly higher than that in the absence of field. However the presence of a magnetic field changes significantly the cross section behavior as a function of kv, especially at low velocities, where reductions of the cross sections and deviations from the 1/kv2 (1/EPscm) are observed. Our calculations show a dependance of the cross section upon the angle between the magnetic field and the flight direction of the incoming Ps∗.
The role of a uniform magnetic field in the collision of two one-electron atoms is analyzed using previously developed density-matrix techniques. During the collision, all magnetic-moment interactions are small compared to the usual singlet and triplet potentials, and the only effect of the magnetic field is to alter the asymptotic states. This effect may be described in terms of the unitary transformation which diagonalizes the Breit-Rabi Hamiltonian. The properties of this transformation are given in detail for electronic spin \textonehalf{} and arbitrary nuclear spin. In addition to presenting a general formulation for this scattering problem, explicit formulas are given for spin exchange in the scattering of polarized beams from unpolarized targets.