spectral series[′spek·trəl ‚sir·ēz]
a group of spectral lines in an atomic spectrum that obey certain laws. In emission spectra, the lines of a given spectral series occur for all the allowed quantum transitions from the various initial upper energy levels of the atom to the same final lower level. In absorption spectra, the lines of a given series occur for the opposite transitions. The wave numbers of the lines in a spectral series obey definite laws and converge to the limit of the series (see Figure 1 in ATOM).
Spectral series can be identified most clearly in the spectra of hydrogen, hydrogen-like atoms, helium, and the alkali metals: the Lyman, Balmer, Paschen, Brackett, Pfund, and Humphreys series for hydrogen, and the principal, diffuse, and sharp series for the alkali metals. (SeeATOMIC SPECTRA.)