APPARATUS FOR SPECTROSCOPIC STUDIES IN THE INTERMEDIATE INFRARED REGION—20 TO 40μ

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Abstract
An infrared spectrometer is described which has the following features: (1) The entire optical path may be evacuated to about 10−4 mm of mercury pressure by the use of charcoal cooled with liquid air. (2) Exit and entrance slits are both adjusted from outside the vacuum by a single graduated head. (3) The optical system is arranged to use one mirror for telescope and collimation with the slits arranged on its optical axis. (4) The prism (or grating) is rotated by a 10‐inch lever actuated by an ordinary micrometer. This lever connecting the prism table, which is in vacuum, with the micrometer which is outside, is sealed by a sylphon tube. (5) By connecting the micrometer head mechanically to a recording galvanometer the spectrometer may be made self‐recording. (6) The spectrometer is constructed in such a way as to give the thermopile maximum isolation from thermal fluctuations in the room. An absorption cell is described which has the following features: (1) The cell has small windows although it will handle a beam having a numerical aperture of ⅓. (2) The radiation path in the absorbing gas is one meter. The cell may be evacuated or it will withstand pressures of several atmospheres. (4) The cell may be heated to 300°C. Various techniques for obtaining monochromatic bands of infrared radiation are discussed. A technique is described which makes spectroscopic measurements possible with a source whose temperature may fluctuate (such as the crater of a carbon arc).

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