THE RESONANCE FLUORESCENCE POLARIZATION OF FREE ROTORS - METHYL IODIDE IN METHANE AND CARBON DIOXIDE

摘要

The polarization of the resonance fluorescence of symmetric top rigid rotors is described by a third-order density matrix treatment of resonance emission and a sum-over-all-rovibronic states scattering-tensor invariant framework. Within this theoretical approach the resonance fluorescence depolarization is a function of the excited electronic stale population and rovibronic coherence decay rates, as well as the electronic absorption/emission line shapes. This description of the depolarization of resonance fluorescence is contrasted with that of resonance Raman in terms of angular momentum selection rules and dependence on material relaxation parameters. In contrast to resonance Raman emission in solution, the accompanying resonance fluorescence polarization is found to be most sensitive to the resonant excited state lifetime when this population decay rime is of the order or less than rotational periods. These effects are demonstrated for excitation resonant with the B-state origin of CH3I vapor in high pressures of CH4 and CO2. The solute-solvent interaction responsible fur the pure dephasing of the resonant optical coherence does not appear to cause orientational redistribution of the excited chromophore, at least on the time scale of the CH3I B-state origin lifetime. The influence of excited electronic B-state rovibrational pure-dephasing effects on the resonance fluorescence polarization measurements are discussed. (C) 1996 American Institute of Physics. [References: 47]