QUANTUM BEAT SPECTROSCOPY
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Publisher:Ohio State University
Quantum beat spectroscopy is a sensitive, selective technique for studying intramolecular interactions between vibrationally hot singlet and triplet states in isolated polyatomic molecules. Quantum beats are oscillations superimposed on fluorescence decay curves and may be analyzed in two limits. A direct perturbation theory approach uses the Fourier transform of the quantum beats to estimate the magnitude of the coupling elements that dictate the intramolecular dynamics which cause the beats. This approach is used in the limit of a low density of interacting states. In the opposite limit we have another approach which utilizes the properties of random matrices and estimates both the density of interacting states and the average coupling element based on characteristics of the time domain data. Application of the experimental technique requires that one be able to: 1) Produce a supersonic nozzle beam of the molecule, 2) Use a sufficiently short time duration, narrow bandwidth preferably single mode laser pulse to excite the molecules, and 3) Time resolve the laser induced fluorescence with a sufficiently large detector bandwidth. The molecules must be chosen such that: 1) The vapor pressure is high enough to form a supersonic nozzle beam. 2) The fluorescence quantum yield is large enough to allow detection, and 3) The density of optically accessible states is large enough so that the laser bandwidth appreciably overlaps more than one state.
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