| The vibrational dynamics of terminal acetylenes and acid dimers have been studied in the gas phase and in dilute solution in an effort to describe the solvent contribution to the relaxation process. The primary technique used in these investigations was ultrafast time resolved pump probe transient absorption spectroscopy. Studying a series of ten terminal acetylenes in five benzene-like solvents and comparing the measured vibrational relaxation to the intramolecular dynamics measured in the gas phase, the simple kinetic model previously developed in our lab to explain vibrational relaxation in solution (kTOT = kIVR + kVER) was found to hold. This simple kinetic model is also a valid description of vibrational dynamics of these terminal acetylenes in the gas phase and in dilute CCl4 at the acetylenic C-H stretch overtone. An in-depth study of cyclopropylacetylene in cold free jet expansion, room-temperature gas, and dilute solution showed an interesting case of exceptionally fast IVR occurring via a tiered mechanism of energy flow which dominated the dynamics, with minor contributions from the solvent. In hydrogen bonded carboxylic acid dimer systems (trifluoroacetic acid and formic acid), where dynamics such as dissociation can occur in addition to the IVR and VER processes, it was found that solvent acted to quench the inherent dissociation dynamics seen in the gas phase. These studies illustrate the contributions that solvent can make to vibrational dynamics in many different systems. |
