Electronic spin multiplicity Excited-state interactions with

A theoretical calculation of the 15N-13C coupling has been carried out (157) by the sum-over-excited states approach using INDO-MO data. The calculation included the Fermi contact, spin-dipolar, and orbital interactions. For the one-bond coupling, the contact term is shown to be dominant, but there are appreciable contributions from the other terms especially when multiple bonding occurs which explains the lack of a reasonable correlation between /(N-C) and the s-electron contribution to the C-N bond. Calculations using the finite perturbation method, together with INDO data, point to a similar conclusion. (212-214)... 

The mechanism of Zeeman relaxation in collisions of molecules in electronic states with nonzero electronic orbital angular momenta is different from that in collisions of E-state molecules. The response of non-E-state molecules to a magnetic field is determined by both the electron spin and the orbital angular momentum of the electrons in the open electronic shell. The orbital motion of the electrons induces electronic anisotropy, which gives rise to multiple adiabatic interaction potentials between the collision partners [20]. Consider, for example, the collision system of a hydrogen atom in an excited P state and a structureless atom, such as He. The interaction between the atoms can be described by an effective potential as a function of the interatomic distance and an angle between the direction of the electronic F-orbital and the interatomic separation line. The angular dependence of this potential is the electronic anisotropy. An alternative description of the interatomic interaction can be... 

---