David Craig

David Craig developed the quantitative theory of splitting in the electronic spectra of molecular crystals, as well as recognising and applying quantitative theory of intensity borrowing, and other characteristic phenomena of very weak transitions. He experimentally identified all these effects in actual examples, the quantitative results establishing assignments of the transitions and distinguishing pure electronic from vibrationally induced bands. He made the first quantitative calculations of band contours in electronic vapour spectra of medium-sized molecules, for example naphthalene. David experimentally observed and identified the bands by their contours, so deducing electronic and vibronic assignments. He made quantitative calculations of intensities in vibrationally induced transitions, and of dimensional changes from intensities. He contributed to pi electron theory in the introduction of configuration interaction into non-empirical molecular orbital theory, and in describing forms of electron delocalisation in non-normal aromatics. He also contributed to the theory of bonds involving d-orbitals in poly-covalent second- and third-row elements.