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Infrared Spectroscopy Chapters 16-17 Chapter 7- I
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IR Selection Rules Change in dipole moment during vibration
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http://www.lsbu.ac.uk/water/vibrat.html Water Vibrations http://chemmac1.usc.edu/Bruno/java/Vibrate.html Carbon Dioxide Vibrations
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FT-IR
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Retardation – difference in path length of two beams
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Interferograms
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Infrared Sources Glowbar Nernst glower Patented sources
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Detectors DLaTGS (pyroelectric) MCT (semiconductor/quantum well) Thermodetectors ( not used for FT-IR, response time is too slow) –Thermocouple –Bolometer –Thermister
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FT Method Advantages 1.Fellget Advantage (Multiplex Adv) –Collect all at once –Faster, don’t need to scan axis 2.Jaquinot Advantage (Throughput Adv) –No slits or optical elements to limit (attenuate) radiation 3.Connes Advantage –Internally calibrated w/ HeNe laser –Wavenumber calibration is: More accurate Better stability
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Black Body Radiation Why don’t we use a light bulb as IR source? According to Black Body Radiation, it should give more intensity in IR region of spectrum.
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ATR / Evanescent wave
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Saturated vs. Unsaturated
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Alcohols
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Ketones and Aldehydes
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Carboxylic Acids
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Ethers
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Esters
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Unknowns
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Raman Spectroscopy Chapters 18
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Elastic scattering Photon scattered at same as incident photon Inelastic scattering Photon scattered at different as incident photon
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e - cloud of molecule can be polarized by E.M. radiation It is possible to induce dipole moment using elect field of E.M. Size of induced dipole depends on polarizability of e - cloud Induced dipole moment polarizability Oscillating electric field
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Raman Selection Rule with vibration Polarizability changes with bond length/vibration Change in bond length
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Gaussian Calculations CO 2 SF 6 Chloroform
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kT I mportant concept in Thermo and Stat Mech
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Vibrational Selection Rules RamanInfrared
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90° Scattering Instrumentation
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Advantages and Disadvantages of Raman Advantages Water is weak scatterer Little sample prep Sharper peaks than IR Use of fiber optics Disadvantages Insensitive (LOD ~ 0.1%) Fluorescence interference –Trade off of / Int / fluor.
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Resonance Raman
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Surface Plasmons – electron oscillations at surface of a metal. Surface Plasmon Resonance – when freq of light photons matches the natural freq of oscillating surface electrons.
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FT-Raman
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Fiber-Optic Raman Spectrometer BP=band pass filter BR=band rejection filter
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Imaging Spectrograph HoloPlex TE Cooled CCD Detector Slit Notch Control Electronics ProbeHead Invictus NIR Laser Kaiser Optical Systems Inc Rxn1 Raman system operating at 785 nm Instrumentation
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Improving Raman Collection Efficiency
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Crystal Hydrate Structure
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Calibration - R AT - R MT
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Phase Transformation upon Water Addition 1838.71700160015001400130012001100977.4 Raman Shift / cm-1 Int immediately 3 min 6 min 9 min 12 min 15 min 18 min
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Apply Calibration to get Kinetic Transformation Profile
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