Molecular electronic transitions

Abstract

This chapter discusses molecular spectra, which are more complex than atomic spectra and convey richer information. It explains how greater complexity arises from the more complicated structures of molecules, for whereas the spectra of atoms are due only to their electronic transitions, the spectra of molecules arise from electronic, vibrational, and rotational transitions. These modes are not independent of one another, and the complexity of the spectra is enriched by the interactions between them. The chapter confirms that an interpretation of molecular spectra yields a great deal of information about the shapes and sizes of molecules, the strengths and stiffnesses of their bonds, and other information that is needed to account for chemical reactions. The energy associated with rotational transitions is usually less than for vibrational transitions, and the energy of vibrational transitions is usually less than for electronic transitions.