Optical emission, far infrared, and Raman spectroscopy are to be used to measure vibrational frequencies in a variety of systems as a function of variables that lead to phase transitions or conformational changes. The interatomic and intermolecular potentials, and changes in them, can be determined from these measurements. The experiments thus provide information about the microscopic mechanisms behind phase transitions or conformational changes in molecular systems. Such information is of fundamental interest in understanding the function of biological systems where conformational changes are of utmost importance.