Precision Measurement
The Rydberg constant is the most well-determined physical constant, with a relative experimental uncertainty of less than 7 parts in 1012. The ability to measure it to such a high precision constrains the proportions of the values of the other physical constants that define it. See precision tests of QED.
Since the Bohr model is not perfectly accurate, due to fine structure, hyperfine splitting, and other such effects, the Rydberg constant cannot be directly measured at very high accuracy from the atomic transition frequencies of hydrogen alone. Instead, the Rydberg constant is inferred from measurements of atomic transition frequencies in three different atoms (hydrogen, deuterium, and antiprotonic helium). Detailed theoretical calculations in the framework of quantum electrodynamics are used to account for the effects of finite nuclear mass, fine structure, hyperfine splitting, and so on. Finally, the value of comes from the best fit of the measurements to the theory.
Read more about this topic: Rydberg Constant
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