Molecular dynamics and a simplified master equation for spectral line shapes

Borrowing heavily from the literature, we develop a transport relaxation eq uation for the off-diagonal elements of the density matrix. It is applicabl e to a large range of topics in laser theory, nonlinear optics and spectral line shapes, etc. Applying this single equation to the case of infrared el ectric dipole transitions permits us to recover, quickly and simply, all of the well-known spectral line shapes found in the literature. It also offer s further insight into the process of line mixing, particularly in the weak mixing limit. An outline of a new treatment of Dicke narrowing and other s peed-dependent contributions to spectral profiles is also given in terms of the transport relaxation equation. The treatment also provides a numerical method for including the effects of statistical correlation between the ev olution of the internal and translational degrees of freedom. [S1050-2947(9 9)11205-8].