Which of the following characteristics pertains to vibrational modes that are Raman active?

Vibrational modes that are Raman active are closely related to changes in polarizability during the vibration of a molecule. Specifically, for a vibrational mode to be Raman active, it must involve a change in the polarizability of the substance as it undergoes that vibration. Polarizability refers to the ability of a molecule's electron cloud to become distorted in the presence of an external electric field, which is fundamental to the Raman scattering process.

When light interacts with a molecule, it can be scattered inelastically, leading to a shift in energy that is indicative of the vibrational modes. The extent to which the polarizability changes with these vibrations determines whether a particular vibrational mode can be observed in a Raman spectroscopy experiment. Thus, the alignment of vibrations with components of molecular polarizability is essential for Raman activity.

Other options do not properly describe the criteria for Raman activity. While vibrational modes might have some relation to symmetry or energy components, these aspects do not directly determine whether a mode will be Raman active. The critical factor is the change in polarizability that characterizes the interaction with light during the Raman scattering process. Therefore, the choice related to molecular polarizability is indeed the defining characteristic of Raman-active modes