Molecular orientation following K-shell photoionization

Molecular-orientation parameters for K-shell photoionization of the N(1s) and C(1s) orbitals of N2 and CO, calculated using Hartree-Fock continuum states, are reported. These studies were motivated by recent measurements of the N(1s) orientation parameter, where substantial shape-resonance enhancement is observed, and by earlier indirect studies of molecular orientation for both N(1s) and C(1s) photoionization via the angular distributions of Auger-electron emission. Through the shape-resonance region nearly isotropic Auger-electron angular factors were obtained by fitting the calculated (continuum multiple-scattering method) molecular-orientation parameters to these latter measurements. However, based on the present results one can extract larger Auger angular factors than previously reported. This supports the earlier prediction of uniquely molecular effects in K-shell Auger processes, i.e., anisotropic emission. In addition, the present results show that to obtain accurate shape-resonance-enhanced molecular-orientation parameters, the Hartree-Fock approximation including relaxation effects must be invoked