ULTRAFAST INFRARED SATURATION SPECTROSCOPY OF CHLOROFORM, BROMOFORM, AND IODOFORM

In this paper we present a study of the vibrational energy relaxation processes of chloroform, bromoform, and iodoform in solution after excitation of the C-H stretch vibration. The relaxation is studied with ultrafast infrared saturation spectroscopy using intense infrared pulses with a pulse duration of 19 ps. The experiments were performed in a polar and a nonpolar solvent in order to study the effects of the polarity of the solvent on the relaxation processes. We observe that in both types of solvent the relaxation takes place via two consecutive relaxation processes and that the relaxation leads to ultrafast changes of the absorption band of the C-H stretch vibrations. We discuss the differences in the time constants of the relaxation processes of the haloforms in terms of the energy differences between the vibrational levels and the interactions with the solvent.