Oscillator Strength

An atom or a molecule can absorb light and undergo a transition from one quantum state to another. The oscillator strength is a dimensionless quantity to express the strength of the transition. The oscillator strength of a transition from a lower state to an upper state may be defined by

$f_{12} = \frac{2 }{3}\frac{m_e}{\hbar^2}(E_2 - E_1) \sum_{m_2} \sum_{\alpha=x,y,z} | \langle 1 m_1 | R_\alpha | 2 m_2 \rangle |^2,$

where is the mass of an electron and is the reduced Planck constant. The quantum states 1,2,..., are assumed to have several degenerate sub-states, which are labeled by . "Degenerate" means that they all have the same energy . The operator is the sum of the x-coordinates of all electrons in the system, etc.:

$R_\alpha = \sum_{i=1}^N r_{i,\alpha}.$

The oscillator strength is the same for each sub-state .

Read more about Oscillator Strength: Thomas–Reiche–Kuhn Sum Rule, See Also

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