Infrared Spectroscopy

Infrared Spectroscopy - AN INTRODUCTION TO INFRA RED...

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AN INTRODUCTION TO . .. INFRA RED SPECTROSCOPY — A self-study booklet — H O H
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INFRA - RED SPECTROSCOPY Introduction Different covalent bonds have different strengths due to the masses of different atoms at either end of the bond. As a result, the bonds vibrate at different frequencies (imagine two balls on either end of a spring) . The frequency of vibration can be found by detecting when the molecules absorb electro-magnetic radiation. Various types of vibration are possible. Bending and stretching are two such examples and can be found in water molecules. Each one occurs at a different frequency. An equivalent bend at 667cm -1 occurs in a carbon dioxide molecule. As molecules vibrate, there can be a change in the dipole moment of the molecule. 2 IR Spectroscopy O H H O H H O H H O O C O H H O H H O H H O H H O H H O H H O H H O H H O H H Dipole Dipole Dipole Normal Distorted Distorted
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The Infra-red Spectrophotometer Operation The intensity of the incident beam and reference beam is measured (they are the same). The intensity of the transmitted beam is also measured. The difference in intensity between the incidence beam and the transmitted beam is a measure of the amount of radiation absorbed by the sample. The frequency of radiation is examined continuously by the monochromator. In the photometer the relative intensities of the reference and transmitted beams are compared; the percentage of the reference beam found in the transmitted beam can be plotted as a function of frequency, or wavenumber. Component parts Source A filament of a rare earth metal oxide or carborundum maintained at red, or white, heat. Optical Path The beam is guided and focussed by silvered mirrors. Ordinary lenses and mirrors are unsuitable because glass absorbs strongly over most of the frequencies used. Any windows must be made from mineral salts (e.g. NaCl) which have been highly polished to reduce the scattering of light. Sample Infra-red spectra can be obtained as follows . .. liquids
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This note was uploaded on 04/26/2008 for the course CHEM 20221 taught by Professor Loyle during the Spring '08 term at Rowan.

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Infrared Spectroscopy - AN INTRODUCTION TO INFRA RED...

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