Coherent anti-Stokes Raman spectroscopy (CARS) is a relatively new kind of Raman spectroscopy which is based on a nonlinear conversion of two laser beams into a coherent, laser-like Raman beam of high intensity in the anti-Stokes region. The emission is often many orders of magnitude greater than normal Raman scattering and, because of the coherent and anti-Stokes character of radiation, the method is very useful for obtaining Raman spectra of fluorescing samples, gases in discharges, plasmas, combustion, atmospheric chemistry. In this paper we outline the basic theory behind CARS and describe its unusual effects and drawbacks. We review the research to date on various materials, and indicate the possible future direction, utility and applications of CARS such as surface studies, fluctuation phenomena, reaction dynamics, photochemistry, kinetics, relaxation, and energy transfer.

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Initial steps for several proposed decomposition mechanisms of NTO have been studied theoretically in order to determine the energies of various reaction intermediates. The methods applied were restricted Hartree-Fock self-consistent field (SCF), single-and double-excitation configuration interaction (CISD), CISD corrected for unlinked quadruple excitations (CISD+Q), and coupled cluster including all single and double substitutions (CCSD) with a double-ζ plus polarization (DZP) basis set. Harmonic vibrational frequencies were computed to characterize the species at the stationary points. The previously reported mechanisms examined include decomposition initiated by C-NO 2 homolysis, migration of ring substituents, and ring-opening processes. On the basis of the energetics of the various schemes, our computations suggest that C-NO 2 bond homolysis is the most probable initial step for unimolecular decomposition of NTO.