Raman Scatterig Explained Scattering occurs when a photon polarises the electron cloud of a molecule and raises it to a “virtual” energy state. Raman scattering occurs if the photons change energy during the scattering process. This is because the excited molecule has relaxed to a higher or lower vibrational state than it had originally. How do you detect the Raman effect? You can measure the Raman effect with a Raman spectrometer. The first step is to illuminate your sample with a single colour of light, such as from a laser. If you were to shine blue light onto a material, you might expect to just see blue light reflected from it. Most of the light that scatters is unchanged in energy (Rayleigh scattered). Only around 1 part in 10 million of the scattered light is Raman scattered. With a Raman spectrometer, you can detect the Raman-scattered light that has changed colour and shifted in frequency. It has changed frequency during the scattering process by interacting with molecular vibrations. Raman scattering occurs because photons (particles of light) exchange part of their energy with molecular vibrations in the material. How does Raman spectroscopy measure vibrational modes? Raman spectroscopy measures the energy difference between vibrational modes by analysing the scattered light. Scattering occurs when a photon polarises the electron cloud of a molecule and raises it to a “virtual” energy state. Raman scattering occurs if the photons change energy during the scattering process. This is because the excited molecule has relaxed to a higher or lower vibrational state than it had originally. Raman scattering is inelastic because photons change energy by interacting with molecular vibrational energy levels. Raman scattering is called ‘Stokes' when the scattered light loses energy. Raman scattering is called ‘anti-Stokes' when the scattered light gains energy. Stokes Raman scattering occurs when the molecule moves from the ground state to a virtual state, before dropping down to a higher energy vibrational state than it had originally. Anti-Stokes Raman scattering occurs when the molecule starts in a vibrationally excited state, moves to a virtual state, before finally relaxing to its ground state. We rarely use anti-Stokes Raman light as it is less intense than the Stokes. However, it does represent equivalent vibrational information of the molecule. In contrast, Rayleigh scattering occurs when the molecule returns to its ground vibrational state. It releases a photon with the same energy as the incident photon. Therefore, Rayleigh scattered light has the same frequency and colour as the incident light. Rayleigh scattering is around 107 times more intense than Raman-scattered light. Modern spectrometers use highly efficient filters to remove the Rayleigh-scattered light. This makes it easy to detect Raman scattering. Thanks for watching Make sure to subscribe and leave a comment below.