Coherent Spectroscopy in Electronically Excited States

Abstract

This chapter deals with one of the new generation of coherence experiments that have been developing in the past few years. In this instance the coherence techniques are applied to levels within electronically excited states, and the coherence is monitored by a double-resonance method. Although the techniques are applicable to many traditional magnetic resonance experiments, they also form the basis for investigating molecular dynamics in spectroscopy and promise to reveal a great deal about the time evolution of excited states and the nature of time-dependent interactions between molecular states in solids. The specific development given here will be confined to coherence experiments in the molecular excited triplet states in zero field; however, it is not too difficult to visualize how the methods could be applied to a wide variety of other systems and problems, some of which are outlined in other chapters of this volume. It is important to stress that the generality of the approach makes it useful to any double-resonance experiment in a multilevel system regardless of whether the levels are associated with spin systems or electronic states, or both, as is the case with optically detected magnetic resonance. For this reason we will develop the theory rather completely.