On the application of state sequence diagrams to the calculation of the Casimir-Polder potential

The Casimir - Polder potential, valid for all intermolecular separation distances outside regions of overlap of molecular charge distributions, as well as its asymptotic forms in the limits of small and large separation, is recalculated using time- dependent perturbation theory with the aid of the newly developed state sequence diagrammatic approach, which, in one picture, represents all time- orderings associated with a specific process. The method is compared and contrasted with the familiar time- ordered graphs due to Feynman, enabling valuable insight to be gained into the nature of virtual photon exchange. While no real calculational advantage is gained by the use of state sequence diagrams in the present application, significant benefits will accrue for other higher- order laser - molecule and intermolecular processes.