Theory of the angular distribution of molecular orbitalK x rays seen in heavy-ion-atom collisions

Dynamical calculations of angular distributions and intensities of two-collision 1s σ molecular orbital x rays in 12–90-MeV Ni + Ni collisions are reported. The Coriolis and spin-orbit coupling between 2pσ and 2pπ and the 3pσ and 3pπ molecular orbitals is included. Due to Coriolis coupling, the molecular wavefunctions and therefore the transition dipoles do not follow the rotation of the internuclear axis in collisions with small impact parameters, but remain approximately fixed in direction. Consequently one can predict the symmetry relations between the laboratoryx, y, andz components of the molecular orbital intensity and therefore the anisotropy of the radiation seen at energies near the united atomK α x-ray line. These relations are used to predict anisotropies of molecular orbital radiation in encounters with large united atom atomic numbers,Z ₁ +Z ₂>137. For Ni + Ni encounters, a lower population of the 2pπ and 3pπ orbitals than the 2pσ and 3pσ orbitals is needed to reproduce the observed anisotropies.