TIME-RESOLVED FLUORESCENCE DEPOLARIZATION IN THE DECAY OF INTERMEDIATE CASE MOLECULES. ZERO-FIELD CROSSING OF THE MOLECULAR EIGENSTATES OF $^{1}B_{3u}$ $PYRAZINE^{*}$

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1983

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Ohio State University

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Pyrazine (1,4-diazabenzene) has been expanded in a seeded supersonic jet of helium and its laser induced fluorescence spectrum recorded following pulsed (and doubled) dye laser excitation to the first excited `singlet’ state. Under these conditions, the decay of the fluorescence is biexponential in character, as expected for an ‘intermediate-case’ molecule. Studies of this decay with simultaneous analysis of the polarization of the emitted light, under ‘single’ rotational level excitation conditions, show that the emission is depolarized nonexponentially in time. This behavior is attributed to dephasing processes by which the initial, non-stationary state evolves into a group of phase incoherent molecular eigenstates, and thus its observation constitutes proof of the coherent nature of the excitation process. $^{*}$Work supported by the National Science Foundation.

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Author Institution: Department of Chemistry, University of Pittsburgh

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