Rydberg–Ritz combination principle

The Rydberg–Ritz combination principle is the theory proposed by Walther Ritz in 1908 to explain the relationship of the spectral lines for all atoms. The principle states that the spectral lines of any element include frequencies that are either the sum or the difference of the frequencies of two other lines.

An atom can be excited to a higher energy state by absorption of a photon with sufficient energy, or decay to a lower energy state through spontaneous emission of a photon. However, according to the principles of quantum mechanics, these excitations can only occur at certain energy intervals. The Rydberg–Ritz combination principle showed how lines of the spectra of elements could be predicted from existing lines. Walther Ritz paper contained the formula.

The NIST database tables of lines of spectra contains observed lines and the lines calculated by use of the Ritz Combination Principle.

The spectral lines of hydrogen had been analyzed and found to have a mathematical relationship in the Balmer series. This was later extended to a general formula called the Rydberg formula. This could only be applied to hydrogen-like atoms. In 1908 Ritz derived a relationship that could be applied to all atoms. This principle, the Rydberg–Ritz combination principle, is used today in identifying the transition lines of atoms.

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