The legacy of Don Madison – electron-atom collisions.

Don Madison was invited to Münster (Germany) in 1984 to carry out calculations for spin-dependent inelastic electron collisions with mercury, a heavy atom with nuclear charge Z = 80. At the time, he appeared to be the one-and-only hope to do this successfully and thereby assist in the interpretation of experimental data taken in the group of J. Kessler and G.F. Hanne. I got involved when Don faced serious problems with the university’s mainframe computer, then the only machine available there for such work. Meeting Don changed my life -- and not just mine when one looks at the many successful students that he taught and the many colleagues around the world that he collaborated with.

In this talk, I will summarize Don’s pioneering contributions to the development and continuous improvement of distorted-wave methods for electron-atom collisions. While those methods were ultimately superseded by non-perturbative approaches for many (but not all) atomic targets, they were transferred to electron-molecule and heavy-particle collisions, where they are still in use today. An important aspect of Don’s work was his continuous desire to understand the physics behind the processes he calculated by switching on and off certain terms in the interaction Hamiltonian. I will present some examples of his ideas.