Spectroscopy Definition

How Is It Different From Spectrometry

A scientist preparing to work with an X-ray photoelectron spectroscopy machine

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Spectroscopy is the analysis of the interaction between matter and any portion of the electromagnetic spectrum. Traditionally, spectroscopy involved the visible spectrum of light, but X-ray, gamma, and UV spectroscopy also are valuable analytical techniques. Spectroscopy can involve any interaction between light and matter, including absorption, emission, scattering, etc.

Data obtained from spectroscopy is usually presented as a spectrum (plural: spectra) that is a plot of the factor being measured as a function of either frequency or wavelength. Emission spectra and absorption spectra are common examples.

How Spectroscopy Works

When a beam of electromagnetic radiation passes through a sample, the photons interact with the sample. They may be absorbed, reflected, refracted, etc. Absorbed radiation affects the electrons and chemical bonds in a sample. In some cases, the absorbed radiation leads to the emission of lower-energy photons.

Spectroscopy looks at how the incident radiation affects the sample. Emitted and absorbed spectra can be used to gain information about the material. Because the interaction depends on the wavelength of radiation, there are many different types of spectroscopy.

Spectroscopy Versus Spectrometry

In practice, the terms spectroscopy and spectrometry are used interchangeably (except for mass spectrometry), but the two words don't mean exactly the same thing. Spectroscopy comes from the Latin word specere, meaning "to look at," and the Greek word skopia, meaning "to see." The ending of spectrometry comes from the Greek word metria, meaning "to measure." Spectroscopy studies the electromagnetic radiation produced by a system or the interaction between the system and light, usually in a nondestructive manner. Spectrometry is the measurement of electromagnetic radiation to obtain information about a system. In other words, spectrometry can be considered a method of studying spectra.

Examples of spectrometry include mass spectrometry, Rutherford scattering spectrometry, ion mobility spectrometry, and neutron triple-axis spectrometry. The spectra produced by spectrometry aren't necessarily intensity versus frequency or wavelength. For example, a mass spectrometry spectrum plots intensity versus particle mass.

Another common term is spectrography, which refers to methods of experimental spectroscopy. Both spectroscopy and spectrography refer to radiation intensity versus wavelength or frequency.

Devices used to take spectral measurements include spectrometers, spectrophotometers, spectral analyzers, and spectrographs.

Uses

Spectroscopy can be used to identify the nature of compounds in a sample. It is used to monitor the progress of chemical processes and to assess the purity of products. It can also be used to measure the effect of electromagnetic radiation on a sample. In some cases, this can be used to determine the intensity or duration of exposure to the radiation source.

Classifications

There are multiple ways to classify types of spectroscopy. The techniques may be grouped according to the type of radiative energy (e.g., electromagnetic radiation, acoustic pressure waves, particles such as electrons), the type of material being studied (e.g., atoms, crystals, molecules, atomic nuclei), the interaction between the material and the energy (e.g., emission, absorption, elastic scattering), or specific applications (e.g., Fourier transform spectroscopy, circular dichroism spectroscopy).