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.

No abstract

Infrared and Raman spectra are presented for the magnesium dihalides isolated in matrices. Of particular interest is the Ramen observation of the ν1 symmetric stretch in argon matrices at 550.0, 326.5, 197.9, and 147.6 cm−1 for MgF2, MgCl2, MgBr2, and MgI2, respectively. For MgF2, ν1 had previously been assigned to a strong infrared feature near 480 cm−1, and this activity (along with isotopic frequency shifts) has been cited as evidence for a nonlinear structure for MgF2. The present results undermine this argument and a linear structure is favored, a result consistent with the failure to detect a dipole moment in gas phase electric deflection measurements. Force constants calculated for a linear structure are compared with values obtained from several theoretical models and the results favor an ion–ion interaction model in which the bonding is essentially ionic. Finally, features due to MgX2 dimers are assigned on the basis of a bridged D2h model, and some features attributed to weak complexes between MgX2 and impurities in the matrix are discussed.

No abstract

No abstract