Analysis of geometrical effects on the behavior of transverse and longitudinal modes of amorphous silicon compoundsWe report on the local order of a-Si 39 C 61 , a-Si 40 C 24 N 36 , and a-Si 26 C 40 N 34 . The total structure factors and pair correlation functions obtained by x-ray diffraction as well as the coordination numbers of the first coordination sphere are presented. All materials exhibit a distinct short range order. In the case of a-Si 39 C 61 , a stoichiometric amorphous SiC phase besides an amorphous carbon phase is formed. Also in the case of a-Si 40 C 24 N 36 and a-Si 26 C 40 N 34 phase separation into two amorphous phases is observed.