In this chapter, we will consider the spectrometer itself. The problem is that no single description of a spectrometer exists. Spectrometers are designed to take advantage of the unique way that different types of light interact with matter. By the same token, most spectrometers have certain common elements. We will consider those elements.
First we will differentiate between the several general classes of spectrometers. Those that deal with absorption and emission phenomena will be considered first. Fourier transform (FT) spectrometers, including resonance spectrometers, will be considered next. Magnetic resonance spectrometers, which use magnetic fields simultaneously with electromagnetic light, will be discussed, as will the marriage of FT with magnetic resonance spectrometers.
Energetically, emission and absorption are opposite processes: in absorption, a photon is taken in by an atom or molecule and causes a process; in emission, a process occurs and produces a photon. (In some forms of spectroscopy, such as Raman spectroscopy, the processes occur together.) In both cases, the important factors to consider are the energy of the photon and how many photons of each energy are involved. This second quantity is the intensity.
Because the same two things are important in both cases, spectrometers for emission and absorption spectroscopy are largely made up of similar components, but in a different order or orientation. For emission or absorption spectroscopy, the following components are necessary: a source of energy or photons, a method of energy differentiation (more about that soon), a sample that absorbs or emits photons, and a detector. Optics are also usually used to manipulate the photons. The source can be a light bulb, a laser, a magnetron, a synchrotron, electricity, a flame, or a hot ceramic rod. Detectors can be a simple heat absorber, photographic film, or light-sensitive electronics. Samples can be anything.
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