Determination of discrete transition multipolarity using the generalized oscillator strength

The generalized oscillator strengths (GOS’s) for quadrupole and monopole (and their sums) excitation of the outer np⃗(n+1)p,(n+2)p levels of the noble gas atoms Ne, Ar, Kr, and Xe are investigated over the broad range of momentum transfer q values, from q=0 up to q=8a.u., the region of their accessibility. The purpose of this investigation is to understand and delineate the relative contributions to the GOS of the various discrete transition multipolarities to guide measurements. This study has been motivated by recent absolute measurements of the GOS’s for the lowest nondipole discrete transition in Ar [X. W. Fan and K. T. Leung, Phys. Rev. A 62, 062703 (2000)] and their subsequent reinterpretation.. The calculations are performed in the one-electron Hartree-Fock approximation and with many-electron correlation effects taken into account within the random phase approximation with exchange for the quadrupole and monopole excitations. We find that the GOS’s for the quadrupole np⃗(n+1)p transitions of Ne, Ar, Kr, and Xe are characterized by two maxima, while the corresponding GOS’s for monopole excitations have only a single maximum.