zero-kinetic energy photoelectron spectroscopy
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چکیده
where S(t) is the measurement, u f & is the final state, used as a ‘‘screen’’ onto which we project the dynamics, m(Q) is the coordinate dependent dipole coupling and uex(t)& is the evolving state that we wish to study. A range of techniques using different kinds of final states u f & have been implemented: time-resolved fluorescence spectroscopy; ionization/mass spectroscopy; stimulated emission pumping; and direct absorption. In general, the choice of the final state must take into consideration several effects: ~1! In order to decompose the evolving wave packet in the basis of the final states, u f & must be well known. In general, however, higher excited states of polyatomic molecules are poorly known; ~2! variation of the dipole coupling between electronic states during the wavepacket evolution will have a strong effect on the measured signals. It is important to choose a technique that ‘‘follows’’ the reaction dynamics, even to ‘‘dark’’ states. ~3! Polyatomic reaction dynamics implies multidimensional wave packets with many frequency components. An integrated detection technique which simultaneously collects all components ~e.g., total fluorescence, total ion yield! may not resolve the complicated underlying dynamics. It is important to develop a differential detection technique that ‘‘disperses’’ or ‘‘isolates’’ the various components, if possible. This was demonstrated successfully using the dispersed fluorescence technique. Time-resolved ionization is a general approach to addresing these issues. Aside from technical advantages such as extreme sensitivity, ionization presents certain conceptual advantages: ~1! The ground state of the ion is often the best known excited state of a polyatomic molecule and can there-
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تاریخ انتشار 1995