Comment on ‘Selection rules for Brillouin light scattering from eigenvibrations of a sphere’

We discuss the selection rules, proposed by Li et al., for Brillouin scattering by acoustic vibration of spherical particles with a size comparable to the wavelength of the exciting light. These rules were based on general group theory, which consider the nature of the electronic transitions (electric dipole, electric quadrupole, ...). They assert that only even spheroidal Lamb modes are active. We show that the selection rules are based only on the symmetry of the displacements and allow all spheroidal Lamb modes to contribute. The derivation of the selection rules for Raman scattering from small particles is also discussed.