How prevalent is Raman scattering compared to Rayleigh scattering?

Raman scattering is indeed a much less common phenomenon compared to Rayleigh scattering, which is why the correct choice highlights its relative rarity. In Raman scattering, photons interact with molecular vibrations, leading to a change in energy and wavelength of the scattered light. This process is inherently less probable than Rayleigh scattering, where photons are elastically scattered without any change in energy, making it significantly more frequent.

The statement that Raman scattering occurs at a rate of approximately one in a million indicates that for every million photons that undergo Rayleigh scattering, only about one will experience Raman scattering. This stark difference highlights the unique but less common nature of Raman scattering in light-matter interactions, making it an important but infrequent tool in spectroscopic applications.

This understanding is crucial in fields such as spectroscopy, where Raman scattering is employed to gain insights into molecular vibrations, compositions, and structures, even though its occurrence is rare compared to the more straightforward and abundant Rayleigh scattering.