Ritz's combination principle
Ritz's combination principle
The empirical rule, formulated by W. Ritz in 1905, that sums and differences of the frequencies of spectral lines often equal other observed frequencies. The rule is an immediate consequence of the quantum-mechanical formula hf = Ei - Ef relating the energy hf of an emitted photon to the initial energy Ei and final energy Ef, of the radiating system; h is Planck's constant and f is the frequency of the emitted light. See Atomic structure and spectra, Energy level (quantum mechanics), Quantum mechanics