Introduction to molecular spectroscopy

After a brief historical introduction, the theory of electronic spectra is discussed. The classification of electronic states and electronic selection rules is given. Energy formulae and selection rules for the vibrational structure and rotational fine structure accompanying an electronic transition are also given. The molecular orbitals for AH2, HAB and AB2 molecules are discussed with the aid of Walsh diagrams. The spectra which were observed for these molecules are summarized together with the molecular geometries which were derived from the analyses of the optical spectra