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Quantum beat effects in the fluorescence decay of the C̃(1B2) state of SO2 have been analyzed in detail and the coupling mechanism, which gives rise to the quantum interference phenomena identified as vibronic mixing with the ground state. The use of transform-limited dye laser pulses for excitation permitted both the sensitive detection of weakly modulated quantum beats and a direct quantitative analysis of the magnitude of the interstate coupling. Small Zeeman shifts were also observed to be present, but because these are less than 1/20 of those observed for singlet–triplet interactions in SO2 and other molecules, they are attributed to indirect coupling effects via the ground state. The onset for predissociation at 218 nm is marked by the disappearance of the quantum beats and both confirms the vibronic coupling model and yields a spectroscopic measure of the ground state dissociation energy. Thus the dynamical behavior of the C̃(1B2) state of SO2 has been uniquely characterized through analysis of the quantum interference effects arising through interstate coupling and is the first such example in the limit of a sparse density of states in a polyatomic molecule.

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The first observations of quantum beat phenomena in the resonance limit of a sparse density of coupled levels in a triatomic molecule are reported.(AIP)

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