Infrared study of goethites of varying crystallinity and particle size: I. Interpretation of OH and lattice vibration frequencies

Abstract A detailed study of the IR spectrum of goethite is given with the aim of relating variations to crystalline order and particle size. The OH stretching vibrations are split into two active components at high frequency, plus two inactive ones at low frequency. Two different bending modes exist from site group splitting. Their active modes from factor group splitting are at lower frequencies than the uncoupled ones. The lattice bands at 630 and 400 cm −1 correspond to Fe-O or Fe-OH stretching, approximately parallel to a and c , and thus respectively sensitive and not sensitive to the particle shape, as long as it remains elongated along c .