Quantum defects determination from experiment

Quantum-chemical ab initio calculations have become an alternative to experiments for determining accurately structures, vibrational frequencies and electronic properties as well as intermolecular forces and molecular reactivity.28-31 Two specific approximations were developed to solve the problems of surface chemistry periodic approximation, where quantum-chemical method employs a periodic structure of the calculated system and cluster approximation, where a model of solid phase of finite size is created as a cutoff from the system of solid phase (it produces unsaturated dangling bonds at the border of the cluster). Cluster approximation has been widely used for studying interactions of molecules with all types of solids and their surfaces.32 This approach is powerful in calculating the systems with deviations from the ideal periodic structure like doping and defects. 

As was discussed in Section IV,A, the quantum chemical calculations allow us to compute the end point of the ft spectrum, provided we know the value of the mass defect of the radioactive nucleus. In later experiments of the ITEP group (Boris et al, 1983) the attained energy resolution of 20 eV made it possible to determine the end point of the /i spectrum EfXax (E0 in notations of the ITEP group). The fitting was done within the energy interval 40-50 eV away from the expected edge of the / spectrum. The value obtained was E0 = 18,579 2.1 eV. 

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