Effects related to pair correlation of π electrons

A good deal has been written about correlation effects of electrons in molecules. We consider a somewhat special type of correlation, viz., the pair correlation of π electrons in large molecules. Various attraction mechanisms which lead to this correlation are discussed. We study the behavior of the large π electron systems in external electric and magnetic fields (i.e., anomalous diamagnetism, polarizability, analog to the Kirkwood formula). It has been shown that in a strong magnetic field pair correlation leads to an additional reduction of the magnitude of the 0-0′ transition. We also consider collective excitations and multiplet structure of the π electron spectrum. Copyright © 1975 American Institute of Physics.