The peak positions, intensities, widths, and shapes all provide useful information Solids, Liquids, gases, semi-solids, powders and polymers are all analyzed Some advantages and disadvantages of infrared spectroscopy are listed in table 2. It is important to know the strengths and weaknesses of infrared spectroscopy so it can be used in the proper way. If the energy of a photon does not meet the criterion in this equation, it will be transmitted by the sample and if the photon energy satisfies this equation, that photon will be absorbed by the molecule.(See Infrared: Theory for more detail)ДЄs any other analytical techniques, infrared spectroscopy works well on some samples, and poorly on others. This condition can be summarized in equation(3) form as follows: The second necessary condition for infrared absorbance is that the energy of the light impinging on a molecule must equal a vibrational energy level difference within the molecule. Infrared active vibrations cause the bands seen in an infrared spectrum. The H-Cl stretch of hydrogen chloride and the asymmetric stretch of CO 2 are examples of infrared active vibrations. Vibrations that satisfy this equation are said to be infrared active. This condition can be summarized in equation(2) form as follows: The first necessary condition for a molecule to absorb infrared light is that the molecule must have a vibration during which the change in dipole moment with respect to distance is non-zero. This is why molecules can be distinguished using infrared spectroscopy. Molecules, like guitar strings, vibrate at specfic frequencies so different molecules vibrate at different frequencies because their structures are different. For example, when a guitar string is plucked, the string vibrates at its normal mode frequency. Fortunately, the complex vibrational motion of a molecule can be broken down into a number of constituent vibrations called normal modes. This is why infrared spectroscopy is a type of vibrational spectroscopy. The bonds can stretch, contract, and bend. When a molecule absorbs infrared radiation, its chemical bonds vibrate. The Electromagnetic spectrum showing the wavenumber of several different types of light. The wavenumber of several different types of light are shown in table 1. Here, we typically refer to light waves by their wavenumber, however it will be more convenient to refer to a light wave's frequency or wavelength. These equations show that light waves may be described by their frequency, wavelength or wavenumber. The frequency, wavelength, and wavenumber are related to each other via the following equation(1): In infrared spectroscopy, units called wavenumbers are normally used to denote different types of light.

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