Transitions future outlooks

Abstract. The current experimental situation regarding tests of fundamental physics using positronium is reviewed. Five measurements are discussed and compared with theoretical predictions the singlet and triplet annihilation decay rates, the ground state and the n = 2 energy intervals, and the Doppler-free two-photon excitation of the IS to 2S transition. Previous results, recent progress (where appropriate), and the outlook for future improvements in these measurements are discussed. 

This review deals with both the theoretical and practical aspects of the use of ESR spectroscopy in molecular sieve science. No attempt has been made to compile an exhaustive list of references to all the work that has been published so far. Rather, we have selected what, we feel, are the most important developments and also, where possible, we have drawn examples from our own work. In a first part, the ESR technique and its extensions such as ENDOR and ESEEM, will be highlighted with special emphasis on the principles of the techniques and the instrumental requirements. Attention will also be given to spectral simulation and to quantitative analysis. In a second part, the general features of ESR spectra of transition metal ions in molecular sieves are analyzed. In addition, some remarks will be made on paramagnetic metal clusters and on paramagnetic molecules. The chapter closes with general conclusions and an outlook into the future. For detailed explanations and discussions-in-depth, we refer to several excellent text books [1-9] and review papers [10-14]. 

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