Terahertz difference frequency response of PdD in two-laser experiments

The cell responded to three difference frequencies in the THz range at 8.2 THz, at 15.1 THz, and at 20.8 THz. The first two of these frequencies can be associated with optical phonon frequencies of PdD with zero velocity. We examine the conjectures that the response at 20.8 THz is due to deuterium in vacancies in the gold coating, or due to hydrogen contamination.