  We investigate line formation of Raman-scattered He II at 4851 in an
expanding neutral spherical shell that surrounds a point-like He II source
located at the center. A new grid-based Monte Carlo code is used to take into
consideration the H I density variation along each photon path. In the case of
a monochromatic He II emission source, the resultant line profiles are
characterized by an asymmetric double peak structure with a tertiary peak and a
significant red tail that may extend to line centers of He II$\lambda$4859 and
H$\beta$. The peak separation corresponds to the expansion velocity, which we
consider is in the range $20-40{\rm\ km\ s^{-1}}$ in this work. Tertiary red
peaks are formed as a result of multiple Rayleigh reflections at the inner
surface of a hollow spherical shell of \ion{H}{1}. Due to a sharp increase of
scattering cross section near resonance, the overall Raman conversion
efficiency is significantly enhanced as the expansion speed increases. In the
case of a He II line source with a Gaussian line profile with a full width at
half maximum of $30 - 70{\rm\ km\ s^{-1}}$, we obtain distorted redward
profiles due to increasing redward cross section of H I. A simple application
to the young planetary nebula IC 5117 is consistent with a neutral shell
expanding with a speed $\sim 30{\rm\ km\ s^{-1}}$.
