Metastable state, decay preparation

Zampedri et al. have shown that, in (100 — x)Si02-(x)Ti02-lEr03/2 planar waveguides prepared by sol-gel route, for x < 12, about 65% of the Er + ions in the Ii3/2 metastable state decay exponentially with a lifetime of about 8 ms (Zampedri, 2003). 

A theory of photochemical processes which relates macroscopic observables to molecular properties should have great appeal to the physical chemist, since in these cases, unlike the case of thermal reactions, the nature of the metastable decaying states can be unambiguously defined. Furthermore, since these states are routinely prepared in photochemical experimentation, they are worthy of extensive study. Perhaps a more complete understanding of the properties of isolated molecule metastable states can play the role of precursor to the understanding of the states involved in thermal reactions. 

In an apparent unimolecular reaction, the molecule is activated in a bimolecular collision process. In addition, it is assumed that the preparation of the initial metastable state of the molecule can be separated from its unimolecular decay. Thus, the apparent unimolecular reaction can also be classified as an indirect reaction. One writes such an apparent unimolecular reaction in the form... 

The decay of the individual quasi-bound (metastable) resonance states follows an exponential law. The wave packet prepared by an ultrashort pulse can be represented as a (coherent) superposition of these states. The decay of the associated norm (i.e., population) follows a multi-exponential law with some superimposed oscillations due to quantum mechanical interference terms. The description given above is confirmed by experimental data. 

The low activation energy of the thermal addition polymerization reaction confirms the necessity of a (librational) motion of the molecules in the initiation process. The first addition process differs from all the following addition proccesses by the metastable monomer diradical structure, which — in contrast to the DR , AC , and DC structures with n > 2 — has a limited life-time given by the phosphorescence decay of the monomer triplet state. Therefore, the librational excitation must be performed during the life-time of the monomer reaction centre. In the case of the low temperature photopolymerization reaction the librational excitation has to be prepared optically via the decay of the electronic excitation. This is in contrast to the photopolymerization reaction at high temperatures, where numerous molecular motions are thermally and stationary present in the crystals. Due to this difference two photons (2hv) are required in every dimer initiation process at low temperatures and only one photon (hv -i- kT) is required at high temperatures. The two paths of the photoinitiation reaction are illustrated below by the arrows in Fig. 26. The respective pair states are characterized by M M and M M as discussed below. 

The well-characterised spin-qubit system of NV defects can be used for the QIT the quantum processor implementation can be realized by the coherent spin manipulation. The first step for coherent spin manipulation is to prepare a pure state of the internal spin structure. For the [N-V]" centre, spin state initialisation can be easily achieved by optical pumping with a polarised laser beam tuned above the absorption band. Decay from the 3E level via optical emission dominates but conserves spin. On the other hand, decay via the metastable singlet level 1A is slower since it does not conserve spin. Competition between those two processes at room temperature leads to spin polarization of the 3A ground level, making populated mainly the ms = 0 substate [40]. Once... 

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