  The non-reversing enthalpy near Tg, DHnr, in bulk GexAsxS1-2x glasses is
found to display a global minimum (~0) in the 0.11 < x < 0.15 range, the
reversibility window. Furthermore, the DHnr term is found to age for glass
compositions both below (x < 0.11) and above (x > 0.15) the window but not in
the window. Glass compositions in the window are rigid but stress-free, those
below the window are floppy, and those above the window are stressed-rigid.
Raman scattering shows floppy and stressed rigid networks to consist in part of
monomers. The latter aspect of structure narrows the width of the reversibility
window and suppresses in part aging effects observed outside the window in
contrast to those in the fully polymerized selenide counterparts.
