Line Mixing Within and Beyond the Impact Approximation

This chapter explores how overlapping lines lead to quantum processes that significantly transform the spectral shape. A naive interpretation would consider each line as independent, assuming that the branch shape can be derived by summing individual line shapes. Experimental measurements of the density dependence of various line-shape parameters justify its applicability to situations involving atmospheric densities. The importance of the limitations defined by the inverse of the collision duration depends on the type of the dominant forces between the colliding partners and varies between two limits. For many molecular systems, the imaginary component of the diagonal elements is much smaller than the real component. A semi-classical model typically treats translational motion classically and internal motion quantum mechanically. The refined Robert Bonamy model is based on the Anderson–Tsao–Curnutte theory from 1962.