13.18 : ラマン分光法: 概要

The Raman effect occurs in molecules whose net bond polarizability changes during vibration. Peaks within the spectrum represent specific vibrational modes of molecules, providing a unique fingerprint for understanding molecular composition and bonding.

In Raman spectroscopy, a high-energy monochromatic laser interacts with a sample. Most of the light is transmitted through it, but a small portion scatters in various directions, which is recorded as a function of wavelength or wavenumber.

The scattered photon's frequency can either match the incident photon's frequency, referred to as Rayleigh scattering, or exhibit a frequency shift, known as Raman scattering.

Raman scattering consists of Stokes scattering and anti-Stokes scattering, where scattered photons have lower frequencies and higher frequencies than the incident photons, respectively. 

The intensity of Raman peaks depends on the bond polarizability, laser intensity, and concentration of Raman-active groups.

However, Stokes signals are almost always stronger than anti-Stokes signals due to the higher population of molecules in the vibrational ground state under most conditions.