In this project in the Theoretical and Computational program of the Chemistry Division, Professor Mead proposes to develop a new general theory to describe the detailed way in which molecules interact with each other and with applied magnetic fields. A general theory will be developed which will enable one to correlate rovibronic states with nuclear spin states for clusters of any size. In addition, the role of Kramers degeneracy will be investigated. The definition and determination of quasidiabatic basis sets, which facilitate computation of coupling between electronic states, will be investigated, as will a new elegant and convenient way of describing the magnetic shielding of the nuclei by electrons.