A theory of vibrational circular dichroism in terms of vibronic interactions

Abstract

A theory of vibrational circular dichroism is developed along the lines of the theory of intensity borrowing by forbidden electronic transitions. The vibrational transition exhibiting circular dichroism is a one-quantum jump in a mode capable of mixing different electronic states. The degree of mixing is different for the initial and final states of the vibrational transition; this is shown to be a source of circular dichroism. The theory is developed on the basis of the adiabatic and crude adiabatic approximations; expressions for rotatory strengths are given. Within the crude adiabatic picture, effects due to any change in the equilibrium configuration on electronic excitation are examined. Vibrational effects in electronic circular dichroism are also analysed.