  The young and compact planetary nebula IC 4997 is known to exhibit very broad
wings with a width exceeding $5000 {\rm km s^{-1}}$ around H$\alpha$. We
propose that the broad wings are formed through Rayleigh-Raman scattering
involving atomic hydrogen, by which Ly$\beta$ photons with a velocity width of
a few $10^2 {\rm km s^{-1}}$ are converted to optical photons and fill the
H$\alpha$ broad wing region. The conversion efficiency reaches 0.6 near the
line center where the scattering optical depth is much larger than 1 and
rapidly decreases in the far wings.Assuming that close to the central star
there exists an unresolved inner compact core of high density, $n_H\sim
10^{9-10} {\rm cm^{-3}}$, we use the photoionization code `CLOUDY' to show that
sufficient Ly$\beta$ photons for scattering are produced. Using a top-hat
incident profile for the Ly$\beta$ flux and a scattering region with a H~I
column density $N_{HI}=2\times 10^{20} {\rm cm^{-2}}$ and a substantial
covering factor, we perform a profile fitting analysis to obtain a satisfactory
fit to the observed flux. We briefly discuss the astrophysical implications of
the Rayleigh-Raman processes in planetary nebulae and other emission objects.
