Photon momentum transfer in one-photon single ionization of helium: The influence of electron correlation

Abstract

The photon momentum transfer in the one-photon single ionization (1PSI) of helium is theoretically and experimentally studied. The influence of electron correlations is found to be displayed in the dimensionless photon momentum-transfer factor F, which takes a value of 8/5 for the 1PSI of the 1s state of hydrogen. For the ground state of helium, we find that F first decreases and then increases with the energy of the photoelectron, which is drastically different from the monotonic behavior predicted by the mean-field approximation. When resonances due to the doubly excited states are accessible, the parameter shows dramatic fluctuations. We report experimental results for F in the energy region of the (2s2p)1P1 and (2p2)1D2 autoionizing states with a photon energy resolution of around 12 meV, a factor of approximately 1.7 better than the resolution reported for the pioneering data of Krässig et al. [Phys. Rev. Lett. 88, 203002 (2002)0031-900710.1103/PhysRevLett.88.203002]. These high-resolution data agree very well with our theoretical predictions. Our study shows that F is sensitive to effects of electron correlations.