Charge transfer in the presence of a magnetic field

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*106 cm s-1 and magnetic field B=0.05 B0 (B0=2.35*105 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.