The effect of collectivized low frequency excitations of adsorbed molecules on the dephasing of their local vibrations

An analysis of temperature-dependent shifts and widths of Davydov-split spe ctral lines for local vibrations in the 2 x 1 phase of CO/NaCl(100) demonst rates that presently accepted theories which neglect the low frequency mode collectivization for adsorbed molecules fail to account for this temperatu re dependence. To provide an adequate description for collectivized modes, a simple formula is proposed which includes, in addition to standard parame ters of the dephasing model, another one, the effective half-width of the l ow frequency vibration band. As a result, a self-consistent treatment of sp ectroscopic data and a parameter determination for the systems studied beco me possible.