Following Gordon, we show that the circular dichroism (CD) spectrum is proportional to the
imaginary part of the Fourier transform of the cross-correlation function of the electric dipole
moment and of the magnetic dipole moment. Such a result is useful in the study of CD band shapes,
and also in obtaining a spectrum from a classical trajectory calculation, as was done for absorption
by Noid, Koszykowski, and Marcus. For ergodic and multiperiodic regimes, the formula reduces to
the Fourier cross spectrum of the two moment functions. As an application, we have run classical
trajectories calculations for two coupled CH stretchings belonging to a chiral HCCH fragment, in
the fixed partial charge approximation. Two sets of results are presented, relative to low and high
total energy: Comments are made about the spectroscopic manifestation of normal, local, and
chaotic modes
