Cyclic population transfer

Ordinary STIRAP is only sensitive to the energy levels and the magnitudes of transition-dipole coupling matrix elements between them. These quantities are identical for enantiomers. Its insensitivity to the phase of the transition-dipole matrix elements renders STIRAP incapable of selecting between enantiomers. Recently we have demonstrated [11] that precisely the lack of inversion center, which characterizes chiral molecules, allows us to combine the weak-field one-and two-photon interference control method [29,54,95,96] with, the strong-field STIRAP to render a phase-sensitive AP method. In this method, which we termed cyclic population transfer (CPT), one forms a STIRAP loop by supplementing the usual STIRAP 1) o 2) <=> 3) two-photon process by a one-photon process 1) <=> 3). The lack of inversion center is essentrat, because one-photon and two-photon processes cannot connect the same states in the presence of an inversion center, where all states have a well defined parity, because a one-photon absorption (or emission) between states 1) and 3) requires that these states have opposite parities, whereas a two-photon process requires that these states have the same parity. 

The photochemical extrusion of nitrogen from cyclic azo compounds has been studied on a broad scale. Cyclic azo compounds, in contrast to acyclic ones can react with N2 elimination from both the Si and the T state. Ring strain as well as the lack of dsjtrans isomerisation favor photodecomposition. Since intersystem crossing is not very efficient the Ti state has mostly been populated by energy transfer. 

The ILIT approach has allowed us to characterize some fast electron transfers between a gold electrode and a surface-attached redox species [1-3]. Data prior to 2001 were analyzed using values of f determined from cyclic voltammetry (CV) and extracting only the value of k° from the k vs. Voc plots. However, those early data have been subjected to spot-check reanalysis as described in Sec. IV.F, and we have confirmed that the values of y determined from CV and from the ILIT experiments agree within experimental error. Thus, we have concluded from this that the CV and ILIT techniques are sampling the same redox population in all cases we have studied. 

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