Single-beam optics

Infrared instruments using a monochromator for wavelength selection are constructed using double-beam optics similar to that shown in Figure 10.26. Doublebeam optics are preferred over single-beam optics because the sources and detectors for infrared radiation are less stable than that for UV/Vis radiation. In addition, it is easier to correct for the absorption of infrared radiation by atmospheric CO2 and 1420 vapor when using double-beam optics. Resolutions of 1-3 cm are typical for most instruments. 

An FTIR spectrometer contains a single beam optical assembly with, as an essential component, an interferometer - often of the Michelson type - located between the source and the sample (Figure 10.7c). It consists of three active components a moving mirror, a fixed mirror and a beam-splitter. 

List the components of a single-beam optical system for absorption spectroscopy. List the components of single-beam optical system for emission spectroscopy. 

Single-beam optics background spectrum collected separately in time from sample spectrum. Can result in error if background spectra not collected frequently... 

Single-beam optics, shown schematically in Figure 2.17, are used for all spectroscopic emission methods. In emission procednres, the sample is put where the source is located in Fignre 2.17. In spectroscopic absorption stndies, the intensity of radiation before and after passing through the... 

The infrared probe uses ATR to obtain the absorption information. The probe crystal is made from a chemically inert material, such as germanium or synthetic sapphire. The reflecting surfaces are masked so that the same area is covered by a sample each time an analysis is made. A single-beam optic system is employed, chopped at 45 Hz. Since the air path is less than 5 cm, as opposed to well over 1 m in conventional infrared spectrophotometers, absorption due to atmospheric water vapor and carbon dioxide is insignificant,... 

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