C+-+How+does+infrared+spectroscopy+aid+in+criminal+investigations?

**By: Jane Ki ** **﻿ **
 * How Does Infrared Spectroscopy Aid in Criminal Investigations? **

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**What is Infrared? **  ü Infrared lies between the visible and microwave portions of the electromagnetic spectrum. ü Ranges of infrared: 1. Near infrared – closest in wavelength to visible light 2. Far infrared – closer to the microwave region of the electromagnetic spectrum ü The portion of the infrared region that is the most useful for analysis of organic compounds has wavelength range from 2,500 to 16,000 nm, with a corresponding frequency range from 1.9x1013 to 1.2x1014 Hz. = near infrared range

ü Covalent bonds are more like stiff springs that can be stretched and bent rather than the sticks found in molecular model kits. ü The bond can vibrate at different amount of energy at a frequency that depends on the masses of the atoms and the strength of the bond. ü As the mass of the atom increases, the frequency of the bond gets lower and lower. ü Stronger bonds give higher frequencies.
 * Covalent Bonds **

ü Infrared spectroscopy is a very simple analytical technique to examine the structures of covalently bonded chemical compounds, such as organic compounds using infrared. ü Most bonds are vibrating at the lowest possible amount of energy at room temperature. But if the radiation of the right frequency is applied, the bond absorbs the energy and vibrates at greater amplitude. ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">Infrared spectroscopy is used to show vibrations at those frequencies depending on the type of the bond. ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">The vibrations are displayed as //wave numbers// in the reciprocal centimeters (<span style="font-family: 'Arial','sans-serif'; font-size: 11pt;">cm-1 ) rather than hertz because the numbers are more manageable. ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">Infrared spectroscopy identifies molecules based on their functional groups rather than giving the exact structure of a compound.
 * <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 16pt;">Infrared Spectroscopy **

<span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt; line-height: 15.6pt; margin: 7.5pt 0cm;">The evidence gathered from the scene can be examined with the infrared spectroscopy: ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">To find clues to a criminal's whereabouts <span style="color: black; font-family: 'Arial','sans-serif';">(“for example, a car model can be found by simply subjecting a paint chip to infrared spectroscopy”) ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">To find postmortem interval (the elapsed time since death). At death, a person’s bones start to lose water, and the proteins begin to decompose. ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">To establish the time when the crime was committed by finding out how aged a bloodstain is. As blood ages, deoxyhemoglobin (HbO) is converted into methemoglobin (MetHb) (red to brown in colour) ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">To analyze drug, fibre, and pain samples ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">To measure blood alcohol content ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">To visualize wounds, such as bruises or bite marks on tissue ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">To detect blood and explosives ü <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 11pt;">Near-IR and Fourier transform IR: used for pharmaceutical forensics, as well as fibre analysis
 * <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 16pt;">How Infrared Spectroscopy is Used in Crime Investigations **

**<span style="font-family: 'Arial','sans-serif'; font-size: 16pt;">Bibliography **

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