Selection Rules and Line Strengths
The results presented in the previous chapter show that, due to the effect of the interaction with the radiation field, the transition probability between two energy levels of an atomic system is, in first approximation, proportional to the square of the magnitude of the dipole matrix element evaluated between the atomic eigenfunctions relative to the levels themselves. In this chapter we will see how this property leads in a natural way to the various selection rules that we presented previously, and we will discuss their limits of validity. We will also see how we can evaluate in a quantitative way the relative strengths of the various lines belonging to a fine-structure multiplet that originates from the transitions between two terms. In Sect. 12.5 we present an application regarding the physical principles that justify the presence of forbidden lines in the spectra of some astronomical objects of particular relevance (solar corona, gaseous nebulae, planetary nebulae, etc.).
- Brink, D.M., Satchler, G.R.: Angular Momentum. Clarendon Press, Oxford (1968) Google Scholar