Momentum space correlation effects in the 23S, 21P and 23P states of He

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Abstract
A Dirac-Fourier transformation of correlated and Hartree-Fock wavefunctions for some (1s, nl) states of He allowed the authors to analyse electron correlation effects in momentum space for excited states of differing symmetry and spin multiplicity. For the 2 3S, 2 1P and 2 3P states, Coulomb shifts and partial Coulomb shifts were determined, as well as certain radial and angular distribution functions. For 2 3S and 2 1P it was established that, like the ground state of He, angular and radial correlation have opposing effects on the momentum distributions. In contrast to this, for 2 3P these two components of correlation work in unison, as occurs in position space. A rationalisation of this behaviour is given, along with an interpretation of the complex nature of the corresponding partial Coulomb shifts. The latter revealed significant changes in the relative importance of angular and radial correlation as the momentum of a test electron was increased. The success of this analysis rested essentially on a detailed knowledge of the inter-vectorial angular shifts. For these excited states, the use of angular expectation values alone proved to be too insensitive to explain the quite marked differences in the correlation characteristics.

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