Applications of nonlinear optics methods in molecular dynamics studies

The possibility of directing the course of chemical reactions by photoexcitation of specific modes of nuclear motion, so called mode-selective chemistry, continues to intrigue physicists, chemists and biologists. This paper addresses the application of stimulated Raman excitation, coherent anti-Stokes Raman scattering, overtone infrared excitation, laser induced fluorescence and multiphoton ionization techniques to the preparation and detection of particular rovibrational states of the parent and product species in photodissociation and reactions of small molecules. Bond- and mode-selective processes in these species are particularly appealing for both theoretical and experimental studies. This is because they are small enough to allow ab initio calculations of potential surfaces and photodynamics and yet retain the complexity of different vibrational degrees of freedom. However, quantitative comparison with theory has required experiments that prepare reactant molecules in specific initial states to avoid the averaging over different quantum states. Also, it is necessary to determine accurately the populations in the various final quantum states of the photofragments.