Theory of collision effects on atomic and molecular line shapes

Abstract

A review of recent developments in the theory of the effects of binary collisions on the spectral profiles associated with atomic and molecular systems is presented. To consistently account for collisional perturbations of both the internal energy levels and the velocity of active (emitting or absorbing) atoms or molecules, one must use a theory in which the center-of-mass motion of the active atoms has been quantized. Following this procedure general equations for absorption or emission line shapes are obtained. The line shapes may exhibit narrowing or broadening with increasing perturber pressure, depending upon the nature of the collision interaction. The physical significance of the collision mechanisms giving rise to such behavior is discussed, as is the experimental evidence in support of the theory. Various applications of the theory are presented.