We propose to observe in the LWS01  and  SWS01  AOT  modes  a
 selected number OH/IR stars. The main purpose  is  to  search
 for silicate and  water ice IR bands in  those  circumstellar
 envelopes. Shapes  and  peak   positions  of  the  bands  are
 strongly sensitive to the structure of  responsible material.
 The structure depends on the thermal history  and/or  on  the
 energetic processes (e.g. ion processing) of the dust  grains
 and of the ice mantles on them. Physical processes  governing
 the birth  and  evolution  of  those  grains  might  then  be
 clarified.