 Inelastic scattering means that the energy of the emitted photon is of either lower or higher energy than the incident photon.After the scattering event, the sample is in a different rotational or vibrational state.For the total energy of the system to remain constant after the molecule moves to a new rovibronic (rotational-vibrational-electronic) state, the scattered photon shifts to a different energy, and therefore a different frequency.