... Aluminum oxide and the opacity of oxygen-rich circumstellar dust in the 12-17 micron range. ... Optical constants: . amorphous alumina (compact/porous) Some details: . ... The optical constants directly obtained from the data by Lorentz oscilator fitting for the range 20-1300 cm -1 correspond to porous alumina. Assiming that the pores are filled with liquid water the optical constants for "compact" alumina were derived using the Bruggeman rule of effective medium theory. ...