Theory of magnetic circular dichroism in molecules oriented by photoselection

Expressions describing the absorption of Light by molecules partially aligned by photoselection in the presence of a static external magnetic field are presented in complete form as a function of the molecular moments acid the polarization properties of excitation and probe beams. The magnetic circular dichroism (MCD) of such samples is shown to involve terms arising from the coupling of electronic transition moments for excitation and probe photons that are additional to terms present in isotropic samples. The theoretical description presented here provides a basis for understanding the nature of MCD signals in samples partially aligned by photoselection and for interpreting the time evolution of MCD measurements when photoselection-induced alignment decays through rotational diffusion. (C) 1996 American Institute of Physics.