| Citation | Distinguished for his experimental studies of electron collisions with atoms and molecules, for associated work in instrument design and for theoretical work on the interpretation of the experimental results. His studies of the influence of molecular rotation and vibration on the angular distribution of scattered electrons have enabled him to deduce the electronic configurations of short-lived molecular negative ion states. He has used the technique of delayed coincidences between electrons and photons for the precision measurements of lifetimes for atomic and molecular states. And he has made major advances in the study of threshold effects in electron collisions, and of post-collision interactions in the near-threshold excitation of resonance states. He has founded a vigorous and independent research school, and by his combination of physical insight and experimental skill has made a unique contribution to his field. |