IR-1 Basics - Infrared Spectroscopy (IR) Basics &...

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Unformatted text preview: Infrared Spectroscopy (IR) Basics & Instruments Molecular Vibration Atoms in a molecule are not fixed in space. They vibrate. To a first approximation, it is like 2 balls, A and B , attached to each other by a spring. If it was really a spring, any energy state would be possible. But, for a molecule, the vibrational energy is quantized. A B Molecular vibration E ground vibrational energy state 1st excited vibrational energy state E vib Electromagnetic Radiation and IR absorption When we put energy into the system, a transition from ground state the the excited state occurs when; E vib = h = c Wave Numbers Typical IR absorptions occur at frequencies ( ) approximately 10 13 s-1 , an inconvenient large number. A more convenient unit, (the wave number in cm-1 ), is used in IR. = c c = speed of light (3 x 10 10 cms-1 ) = 1 = wavelength Also, Classic IR Instrument I ref I sample %T = I sample I ref x 100 Or, use absorbance (A) A = - log ( ) I ref I sample l : light intensity A Typical IR Spectrum E vib is related to bond strength, mass of atoms etc Structual analysis %T Wavenumber (cm-1 ), reciprocal centimeter FT-IR Instrument...
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This note was uploaded on 01/18/2012 for the course CHEM 460AB taught by Professor Sasaki during the Fall '11 term at University of Washington.

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IR-1 Basics - Infrared Spectroscopy (IR) Basics &...

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