Intramolecular Vibrational Energy Transfer and Bond-Selected Photochemistry in Liquids

摘要

The research described in this Final Report was directed toward measuring the time for energy flow within isolated molecules and in molecules in solution. The approach was to use a 100-fs pulse of light from a Ti:sapphire laser to pump two optical parametric amplifiers in order to generate infrared pulses, for exciting vibrations, and ultraviolet light, for exciting electronic transitons. In the gas phase experiments, one pulse excited the first overtone of the O-H stretching vibration in nitric acid and the second pulse probed the excited molecule by excitation to a dissociative electronic surface, which led to the production of electronically excited products that emitted light. The experiment showed that the flow of energy out of the O-H stretch takes about 12 ps. In the liquid experiments, the infrared pulse excited the first overtone of the C-H stretch in methylene iodide and the ultraviolet pulse probed the molecule by transient absorption. The flow of energy within the molecule took about l0 ps, and the flow of energy into the solvent took between 70 ps (in carbon tetrachloride) and 30 ps (in benzene) depending on the solvent.