RayClouds Photoelectric Technology Co.,Ltd.
RayClouds Photoelectric Technology Co.,Ltd.

Principle and Difference between Raman Spectrometer and Infrared Spectrometer

Raman spectrometer and infrared spectroscopy are powerful tools for the study of molecular structure and configuration, material composition identification, and structural analysis. Due to their non-destructive, high sensitivity, and short detection times, they have a wide range of applications in physics, chemistry, biology, mineralogy, archaeology, and industrial product quality control.

Principle and Difference


(1) Raman Spectrometer

When light hits a material, photons collide with electrons in molecules, and inelastic collisions occur, and some of the energy of the photons is transferred to the electrons. In this case, the frequency of the scattered light is not equal to the frequency of the incident light. The scattering is called Raman scattering, and the resulting spectrum is called the Raman spectrum. Raman spectroscopy is a method by which information on the internal structure of molecules can be obtained by measuring the change in frequency of the scattered light relative to the incident light.

(2) Infrared Spectrometer

When a sample is irradiated with infrared light of continuously changing frequency, molecules absorb certain frequencies of radiation, and the net change of dipole moment caused by its vibrational or rotational motion, the resulting molecular vibration and rotational energy level jump from the fundamental state to the excited state, so that the intensity of transmitted light corresponding to these absorption regions is weakened. Plotting the measured absorption intensity against the wavelength or wavenumber of the incident light is the infrared spectrum. The method of structural analysis, characterization, and quantification using the selective absorption of radiation in the infrared region of the material is called infrared absorption spectroscopy.

Raman spectroscopy and infrared spectroscopy exist as complementary techniques in analytical techniques.

Common to both:

Both are infrared absorption frequencies equal to the Raman shift for a given chemical bond, and both represent the energy of the first vibrational energy level. Thus, for a given compound, some peaks have identical IR absorption wavelengths and Raman shifts, and both IR absorption wavelengths and Raman shifts are in the IR optical region, both of which reflect structural information about the molecule. Raman spectroscopy, like infrared spectroscopy, is used to detect the vibration and rotation energy levels of molecules of matter.

Differences and comparisons

Infrared Spectrometer
Raman Spectrometer
MechanismsVibration-induced changes in the dipole moment or charge distribution of moleculesDue to the transient deformation of the electron cloud distribution on the bond causing temporary polarization, a change in the polarization rate produces an induced dispole, which scatters when returning to the fundamental state.
Detection Range400-4000cm-140-4000cm-1
Spectral Generation MethodAbsorption SpectroscopyScattering Spectroscopy
Detecting ObjectsDipole moments of chemical moleculesElectron cloud polarization of molecules
Testing Requirements

Neste lamps, silicon carbide rods, etc. as light sources

Samples require pre-processing

Laser Light Source

Samples do not require pre-processing

Sample RequestStrong absorption of water, severely affecting test results and limiting applicationsphamaceuticals, chemicals, etc.
Mapping InformationReflective molecular functional groupsReflects the molecular skeleto and analyzes biomolecules.

Difference between Infrared Spectroscopy and Raman Spectroscopy Detection Mechanisms

Dipole Moment VariationInfrared SpectrometerRaman Spectrometer
obviousStrong Absorption PeakWeak Absorption Peak
not obviousWeak Absorption PeakStong Absorption Peak
almost noHardly everStrongest Raman Peak

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