6 - Magnetic electronic optical activity

Summary

I have succeeded in magnetizing and electrifying a ray of light, and in illuminating a magnetic line.

(Michael Faraday)

Introduction

This chapter is concerned mainly with the visible and near ultraviolet optical rotation and circular dichroism that all molecules show in a static magnetic field. Magnetic optical activity is generated by appropriate components of α′_αβ, the imaginary part of the complex dynamic polarizability tensor. As discussed in Chapter 4, α′_αβ is time odd and can only contribute to birefringence phenomena in the presence of some external time-odd influence. This chapter deals mainly with a liquid or solution sample in a static magnetic field, which constitutes a uniaxial medium for light propagating along the field direction.

The formulation of magnetic optical rotation and circular dichroism developed below is based on an article by Buckingham and Stephens (1966), which is itself based on Stephen's dissertation (1964). Although the correct quantum mechanical description had been given much earlier by Serber (1932), it was the Buckingham–Stephens work that initiated a new era in magnetic optical activity, at least in chemistry.

Since magnetochiral birefringence and dichroism are generated by appropriate components of the time-odd molecular property tensors G_αβ and A′_{α, βγ} in a static magnetic field collinear with the propagation direction of the light beam in a manner analogous to the generation of magnetic optical activity through α′ _αβ, a quantum mechanical theory of these effects is also developed in this chapter.