The adsorption of PF3 on Cu(001) was studied by means of high resolution helium atom scattering (HAS) and SPALEED. PF3 adsorbs at surface temperatures below 210 K and forms a lattice gas at exposures less than 0.8 L. Saturation is reached for exposures greater than 3 L. At these coverages PF 3 forms an ordered c(4 x 2) layer for surface temperatures above 145 K. For temperatures below 145 K an incommensurate, hexagonal PF 3 layer was observed that necessarily excludes uniquely on-top site PF3 molecule to surface coordination. A new vibrational mode in the thermal energy regime corresponding to the frustrated translation parallel to the surface was identified; the energies of excitation were 3.3 meV and 3.5 meV, respectively, for the isolated molecules and the c(4 x 2) structure. No dispersion of the frustrated translation in the ordered c(4 x 2) phase was found. The results are discussed in terms of adsorbate-adsorbate and adsorbate-substrate interactions.