Abstract
We have constructed the ATR (Attenuated Total Reflection) apparatus, goniometer, to determine accurately the two bulk optical constants, refractive index and absorption index, of substances in condensed phases in the infrared region.Rotation of the source optics is controlled by a 100 mm diameter worm wheel and a micrometer drive graduated to read to 1'of arc.The average angle of incidence can be varied from 15° to 90° and be determined better than +6'. We used a Perkin-Elmer model 13 single-beam spectrometer equipped with LiF, NaCI, KBr and CsBr prisms in various spectral regions.A chopper was placed between sample and source so that the effect of emission from sample could be eliminated. We calculate the optical constants from the observed reflectivities at two angles of incidence by a“brute force”method of solution programmed in FORTRAN IV.The two angles are chosen so that they give widely separated reflectivities which are quite sensitive, but not too sensitive, to small changes in the angle.Construction, alignment and performance are described.Data are presented for the liquid chloroform ν5and the dichloromethae ν8.
