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Radiation Interaction with Molecules

  1. John R. Lombardi

Published Online: 15 JUL 2005

DOI: 10.1002/3527600434.eap376.pub2

Encyclopedia of Applied Physics

Encyclopedia of Applied Physics

How to Cite

Lombardi, J. R. 2005. Radiation Interaction with Molecules. Encyclopedia of Applied Physics. .

Author Information

  1. The City College of New York, Department of Chemistry, New York, USA

Publication History

  1. Published Online: 15 JUL 2005


Various aspects of the interaction of electromagnetic radiation with matter are explored. The fundamental interaction involves the response of matter to electric and magnetic fields generated by the radiation. Any collection of charged particles will respond through its polarization P, which may be expanded in increasing powers of electric field E as P = χ(1)E + χ(2)E2 + χ(3)E3. The term χ(1) is called the linear susceptibility (or more commonly the polarizability α), and is the term responsible for the linear refractive index as well as for linear absorption. The first order susceptibility is shown to be responsible for normal one-photon spectroscopy, and we examine microwave, infrared, and optical spectroscopy as tools to obtain information as to the rotational, vibrational, and molecular orbital nature of molecules. Rydberg states, vibronic interactions, and magnetic resonance spectroscopy are also considered. χ(2) is the second-order polarizability, sometimes called the hyperpolarizability β. This is responsible for hyper-Rayleigh scattering and second-harmonic generation, as well as the hyper-Raman effect. These are often termed two-photon effects owing to the quadratic dependence on the electric field. Three-photon effects are obtained from the third-order polarizability χ(3) or γ. Stimulated Raman spectroscopy and four-wave mixing are some of the most important consequences of this term. These involve coherent anti-Stokes Raman scattering (CARS) as well as Raman-induced Kerr-effect spectroscopy (RIKES).


  • molecular spectroscopy;
  • microwave spectroscopy;
  • infrared spectroscopy;
  • optical spectroscopy;
  • Raman spectroscopy;
  • Rydberg states;
  • multiphoton spectroscopy;
  • second-harmonic generation;
  • coherent anti-Stokes Raman scattering (CARS)