Studies in infrared spectroscopy

The modernization of a vacuum grating infrared spectrometer is described. Experiments using this spectrometer on N-methyl formamide in the vapor phase are described, and the results are interpreted in terms of the position, shape, and intensity change with temperature of the vibration bands of this substance. It is concluded that N-methyl formamide exists in two isomeric forms in the vapor phase. The less abundant form is the cis isomer which lies 1.4 kcal. above the trans isomer. An echelle-type grating used with this spectrometer is shown to have an unusually wide and flat efficiency curve. This is ascribed to a scattering phenomenon in which both faces of a groove participate. Mathematical analyses based on both the Kirchhoff theory and on the Rayleigh theory are shown to predict the broad region of high efficiency for this grating. An amplifier which is intended to be used with a novel double-beam ratio detection system is described.</p