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What Is an IR Spectrum Database?

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  • Written By: Maggie J. Hall
  • Edited By: Susan Barwick
  • Last Modified Date: 26 November 2014
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An infrared, or IR, spectrum database contains information about the reaction between infrared light and inorganic and organic substances. Molecules absorb infrared light in varying degrees based on their overall structure. Using spectroscopy, researchers graph these results and submit them into the IR spectrum database. Chemists, forensics specialists, and researchers often test unknown substances and compare the results with the database, resulting in a positive identification.

Compared to the visible light spectrum, infrared light has a longer wavelength and a lower frequency. Scientists further break down the spectrum into three sections, the near, middle, and far. Molecules constantly move and vibrate. When exposed to infrared light, portions of the molecules may absorb the light when electrical frequencies match those of the infrared spectrum. Spectroscopy measures the absorption levels and displays the results on an interpretative graph.

The horizontal line of the graph represents frequencies in the infrared spectrum. The vertical axis denotes the percentage of transmitted light. Nonabsorption appears as a line running horizontally across the top of the graph, illustrating 100 percent of the beam. As compounds or substances absorb the light, molecules vibrate. Scientists call the specific movements the molecules exhibit by terms that include rocking, scissoring, and stretching.

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These movements appear on the graph as a line dipping down, creating inverted peaks, that stop at the percentage level of remaining infrared light. Scientists call these peaks and valleys bands. The length and width of the bands depends on the absorption rate, the intensity, and the type of movement displayed. Different compounds display bands unique to that substance, acting as a fingerprint for identification. An IR spectrum database contains the graphs of these bands of tested compounds.

When testing unknown substances, the IR spectrum database, contained within spectroscopes, generally compares test results with known data and identifies compounds within the substance. The IR spectrum database is also useful for validating the presence of suspected substances, including alcohol. Forensic scientists regularly use infrared spectroscopy and IR databases to identify drugs, fibers, and paint specimens. By analyzing bone cells of a deceased individual using IR technology, forensic specialists can determine time of death.

Pharmaceutical industries often refer to an IR spectrum database for determining the type and purity of herbs contained in over-the-counter supplements. Biological researchers require the information when determining the presence of pollutants in the environment. Using spectroscopy and an IR spectrum database, analysts often determine the identity of gases, liquids and solids.

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