  An important source of opacity in exoplanet atmospheres at short visible and
near-UV wavelengths is Rayleigh scattering of light on molecules. It is
accompanied by a related, albeit weaker process -- Raman scattering. We analyze
the signatures of Raman scattering imprinted in the reflected light and the
geometric albedo of exoplanets, which could provide information about
atmospheric properties. Raman scattering affects the geometric albedo spectra
of planets in following ways. Firstly, it causes filling-in of strong
absorption lines in the incident radiation, thus producing sharp peaks in the
albedo. Secondly, it shifts the wavelengths of spectral features in the
reflected light causing the so-called Raman ghost lines. Raman scattering can
also cause a broadband reduction of the albedo due to wavelength shifting of a
stellar spectrum with red spectral index. Observing the Raman peaks in the
albedo could be used to measure the column density of gas, thus providing
constrains on the presence of clouds in the atmosphere. Observing the Raman
ghost lines could be used to spectroscopically identify the main scatterer in
the atmosphere, even molecules like H$_2$ or N$_2$ that do not have prominent
spectral signatures in the optical wavelength range. If detected, ghost lines
could also provide information about the temperature of the atmosphere. In this
paper we investigate the effects of Raman scattering in hydrogen- and
nitrogen-dominated atmospheres. We analyze the feasibility of detecting the
signatures of Raman scattering with the existing and future observational
facilities, and of using these signatures as probes of exoplanetary
atmospheres.
