Line Emission Processes

Abstract

In this chapter, we will review the sometimes arcane, frequently confusing, notations that are used to classify atomic and molecular transitions and spectra. A basic understanding of these is essential, since it is through the atomic and molecular lines that we ultimately derive our understanding about the physical conditions in, and chemical abundances of, diffuse astrophysical plasmas. In what follows, we will assume that the reader is familiar with the basic concepts of quantum mechanics. If not, the reader is referred to the highly readable account of this and other topics in modern physics which is in the book by Rohlf (1994). Also, a lucid introduction to molecular spectroscopy is given by Atkins (1983); see notes on this chapter.

“All Science is either physics or stamp collecting”

— Ernest Rutherford