ANALYSIS OF CR3-PARAMETERS - AN APPRAISAL OF THE METHOD BY LUO AND HUANG( OPTICAL)

The method reported by Luo and Huang (J. Phys.: Condens. Matter 1993 5 9411) for analysing the optical data of Cr3+ complexes, which uses on ly a coupling to one single vibrational mode is discussed. Taking as a guide the case of the CrF63- complex it is pointed out firstly that t he frequency omega used in the method has no direct physical meaning, being smaller than those associated with A(lg) and E(g) modes observed in optical spectra, and secondly that the assumed relation between 10 Dq and the Stokes shift E(s) is in general not true as it is only vali d for the partial contribution of the A(lg) mode to E(s). Despite thes e facts it is also explained that no unreasonable band-width values ca n be predicted provided that the fitted values of the Huang-Rhys facto r and the frequency reproduce the experimental Stokes shift. In conclu sion the proposed method of Luo and Huang is shown to be not conceptua lly right, giving rise to a worse description than that achieved throu gh the coupling to the two A(lg) and E(g) modes of the CrF63- complex.