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Time-dependent Emission Spectra from Molecular Wave Packets

Wave packet states of atoms and molecules play an important role in studying the boundary between the classical and quantum domains. Such states are essentially nonstationary. Characterizing them requires determining the dynamics of the probability distribution of the particular degree of freedom in which the wave packet is excited. One way to accomplish this goal is to track the wave packet via the time-dependent spectrum of spontaneous emission. We have performed such measurements for a wave packet in the nuclear degree of freedom of a sodium dimer. This technique permits tracking of the nuclear wave packet in a single excited electronic state over a substantial fraction of its periodic trajectory. It has important applications for studying wave packet excitations in quantum confined electronic microstructures and larger molecules.