  Raman spectra of GexAsySe100-x-y (0 < x < 30; 10 < y < 40) glasses have been
studied at room temperature. Three sets of samples were investigated; it was
revealed that they are qualitatively differing by shape of their spectra. The
structure model was proposed for glasses of each set. The selection of the
glasses on the sets with the same structure type can be made using the formal
parameter - the mean coordination number <m> (the mean number of covalent bonds
per atom): i) 2.1 < <m> < 2.51 (polymeric structure); ii) 2.51 < <m> < 2.78
(molecular-cluster structure); iii) 2.78 < <m> < 3 (network structure).
