| Vibrational energy relaxation (VER) and vibrational cooling (VC) of polyatomic liquids are studied with the ultrafast Infrared-Raman (IR-Raman) technique. In the IR-Raman technique, a type of two-dimensional vibrational spectroscopy, a vibrational transition is pumped with a mid- infrared pulse and the instantaneous populations of all Raman-active transitions are simultaneously probed via incoherent anti-Stokes Raman scattering of a time-delayed visible pulse. The theoretical framework for these measurements, including force-force correlation function methods and perturbative techniques is reviewed. Experimental aspects of the IR-Raman technique are discussed, including laser instrumentation, experimental set up, the nature of the pumping and probing processes, detection sensitivity and optical background, and the interpretation of results including spectroscopic artifacts. Then examples are provided from recent research, focusing on timely problems such as the pseudo vibrational cascade, the dynamics of doorway vibrations, dynamics of overtones with Fermi resonance, multiple vibrational excitations via combination band pumping, and spectral evolution in associated liquids.; This research was supported by U.S. Army Research Office contract DAAH04-96-1-0038 and Air Force Office of Scientific Research contract F49620-97-1-0056. Partial support is acknowledged from National Science Foundation grant DMR-9714843. I wish to also acknowledge support from AASERT fellowships DAAH04-95-1-0284 and DAAG5-98-1-0191. |
