Theory of Quantum Beats and Emission Dynamics from Molecules
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The theory and experimental study of molecular emission is of fundamental and applied significance. New interesting problems arise as more state-of-the-art technique for producing molecules in well isolated state (e.g., by supersonic jet cooling) and more sophisticated laser excitation sources are developed. Figure 1 shows a typical level scheme involved. The ground singlet state is radiatively coupled to the excited singlet state, but not to the manifold of triplet excited states. Depending on the density of these triplet states (which are coupled to the excited singlet by spin-orbit interactions), the emission from the molecules (from the coupled singlet-triplet excited states) may be classified roughly into the “small”, the “intermediate” or the “statistical” limitsl defined by YTρT ≪1, YTρT≤ 1 and YTρT≫ 1, respectively, where YT is the decay rate (line-width) of the triplet and ρT is the density of the triplet levels).
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- 1.See, for example, H. Saigusa and E.C. Lim, Rotational modulation of fluorescence decay and quantum beats in expansion-cooled azabenzenes: Small molecule behaviour of rotatignlly cold S-triazine in the lower vibronic levels of the A E state. J. Chem. Phys. 78, 91 (1983).Google Scholar
- 2.See, for example, F. Lahmani, A. Tramer, and C. Tric, Nonexponential decay in single vibronic level fluorescence: A comparison between kinetic and quantum mechanical method, J. Chem. Phy. 60, 4431 (1974).Google Scholar
- 3.I.C. Khoo and J.H. Eberly, Emission rate of a multilevel atom and its quantum beats, Phys. Rev. A14, 2174 (1976).Google Scholar