Quantum theory of radiative transition phenomena

An elementary account is given of the absorption and emission of radiation by molecules employing a particular formulation of Schroedinger theory which facilitates the treatment of radiative line widths and level shifts. The familiar Fermi golden rule for transition rates, the Rabi--Bloch--Siegert absorption profile, and the Weisskopf--Wigner approximation for spontaneous decay are obtained under appropriate conditions in the context of a common perspective. Comparisons are made with other recently devised perturbative and nonperturbative formulations of electromagnetic transition phenomena which correctly include radiative line widths and level shifts, and the importance of proper treatment of the normalization and phase of the Schroedinger wave function in this connection is emphasized