  The $5p$ two-photon ionization cross section of xenon in the photon-energy
range below the one-photon ionization threshold is calculated within the
time-dependent configuration-interaction-singles (TDCIS) method. The TDCIS
calculations are compared to random-phase-approximation (RPA) calculations
[Wendin \textit{et al.}, J. Opt. Soc. Am. B \textbf{4}, 833 (1987)] and are
found to reproduce the energy positions of the intermediate Rydberg states
reasonably well. The effect of interchannel coupling is also investigated and
found to change the cross section of the $5p$ shell only slightly compared to
the intrachannel case.
