587 08 wk05b spectroscopy std

587 08 wk05b spectroscopy std - Spectroscopy, Why....

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1 Spectroscopy Basics Chemistry 587 •Spectroscopy, Why… absorption of radiation –Atomic –Molecular » Molecular vibrations, … » Molecular Degrees of Freedom » Beer’s Law » •Electromagnetic Radiation • Blackbody radiation – blackbodies – radiation sources used in experiments • wave properties – amplitude – wavelength – propagation – polarization –c = ν λ • wavelength regions and associated energies » gamma, X-ray, vacuum UV, UV, IR, microwave … • diffraction • coherent radiation • refraction – Dispersion = refractive index variation of a medium with the wavelength or frequency – Snell’s Law • reflection • scattering – Rayleigh – Raman – Bandwidth and the Uncertainty Principle – Relaxation processes (after absorption) 320 3100 3000 2900 2800 2700 Wavenumber (cm -1 ) 2939 2971 υ a (CH 3 ) 3052 υ (=CH) 2900 υ s (CH 3 ) 2922 3004 2 υ (C=C) 2850 2733 2 δ s (CH 3 ) http://www.wag.caltech.edu/home/jang/genchem/infrared.htm The energy diagram to the right: Longer lines = higher energy transitions Why should we learn about light waves? - Molecules absorb specific frequencies of light.
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2 Photon Absorption by the Molecule http://www.wag.caltech.edu/home/jang/genchem/infrared.htm For vibrational (IR) spectroscopy, Beer’s Law applies A = ε bc T = P/P 0 ,so, Group frequency correlation chart for Infrared spectrum of 2-propenenitrile
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3 A Classical Mechanics Model of Molecular Vibration “The Harmonic Oscillator” Using a Diatomic Molecule (for example: N 2 or HCl) A spring! With an object dangling from one end F = - ky (Hooke’s Law) F = force to restore to the original position y = distance from the equilibrium position k = force constant, k describes the stiffness of the spring The force, F, tends to restore the object to its original position
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This note was uploaded on 07/17/2008 for the course CHEM 587 taught by Professor Allen during the Spring '08 term at Ohio State.

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587 08 wk05b spectroscopy std - Spectroscopy, Why....

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