Dephasing of local vibrations of a two-dimensional dipole system

Anharmonically coupled, high-and low-frequency branches of vibrational excitations of a two-dimensional dipole system on a substrate are studied. It is shown that independent low-frequency resonance modes characterized by a two-dimensional wave vector belonging to the first Brillouin zone of the dipole lattice arise as a result of the harmonic interaction of phonons in the dipole system and in the substrate. The positions and widths of the spectral lines of the high-frequency local vibrations, which in the general case depend on the dispersion laws and lifetimes of the resonance modes, are calculated for low-temperature orientational states of degenerate dipoles on triangular and square lattices. (C) 1998 American Institute of Physics.