Infrared (IR) reflectance and absorbance spectra obtained from polycrystalline and single-crystal perovskites of MgSiO3 and (Mg0.9Fe0.1)SiO3 composition yielded virtually all the expected fundamental modes. Near-IR absorbance spectra indicate that the polycrystals were anhydrous, whereas the single crystal contained about 0.06 wt % H2O. A Kieffer-type model was used to calculate heat capacity, entropy, and Debye temperature for the orthorhombic perovskite phase. The calculated values at 298 K are Cp=82¿2 J/mol K and S-56¿2 J/mol K. Our calculated Cp agrees with calorimetric data within 5%. Above 500 K, the Debye temperature is nearly constant and equals 960¿30 K. The bulk modulus is calculated from vibrational frequencies to be 265¿13 GPa which lies within 2% of recent experiments. The Clapeyron slope for the phase transition between ilmenite and orthohombic perovskite is calculated to be 1.1¿0.6 MPa/K which is close to the experimental determination. ¿ American Geophysical Union 1994