Comparison of the Landau-Zener Theory with Measurements of Electron Capture inB3++ He Collisions

An experimental total cross section for single-electron capture by heliumlike ${\mathrm{B}}^{3+}$ from He has been measured at relative velocities between 0.7 and 7.4 × ${10}^7$ cm/sec (300-eV to 31.5-keV ${\mathrm{B}}^{3+}$ laboratory energy), and has been compared with a cross section calculated via the Landau-Zener theory. In the velocity range considered, the dominant crossing of the (B + He${)}^{3+}$ system is between $s$ states and the often-neglected conditions for applicability of the theory are met. The velocity positions of the cross-section maxima are in agreement, but the experimental magnitude at maximum is greater by a factor of 2.