Chapter 74 Atomic theory and optical spectroscopy

Abstract

This chapter provides an overview of atomic theory and optical spectroscopy. What follows is an attempt to trace the history of optical lanthanide spectroscopy and the role it has played in the development of atomic theory. Two intertwining strands have to be described: free-ion spectroscopy and crystal spectroscopy. To keep the latter to manageable proportions no account is given of effects depending on more than a single lanthanide ion. There is also no detailed cataloguing of experimental or theoretical results; the aim throughout is to give priority to the development and assimilation of ideas. In 1935, theory came in two forms: with group theory and without group theory. Every theorist was conscious of this dichotomy. It is probably impossible to recapture the partisan character of the early articles on atomic theory, though the passions that the methodology aroused are obvious enough. Atomic multiplets are treated by wave mechanics, without using group theory.