ABSTRACT
Typically, the optical activity is a notoriously weak effect since it involves an interaction of magnetic dipole with external magnetic field. This renders the timeresolved optical activity (CD and ORD) spectroscopy experimentally difficult, even though the time-resolved CD or ORD spectroscopy is capable of providing crucial information on the structural changes of biomolecules in the processes of their functions. In the vibrational frequency domain, two important optical activity measurement methods have been used. The first is an infrared analog of electronic CD, which has been called the vibrational CD (VCD).2, 3 The second is the Raman optical activity (ROA), which is an optical activity version of Raman scattering spectroscopy.1, 4, 5 Much like the relationship between IR absorption and Raman scattering, the VCD and ROA techniques are complementary to each other. In addition to these two vibrational OA measurement methods, one can also use singly vibrationally resonant nonlinear optical spectroscopy to study chiral nature of molecules in solution, as will be discussed later in this chapter. All these optical activity measurement methods can be considered as a particular class of linear response spectroscopy, and the corresponding linear response functions averaged
over randomly oriented chiral molecules in solutions will be presented and discussed here.
