Infrared Spectroscopy Chapters Chapter 7- I

IR Selection Rules Change in dipole moment during vibration

Water Vibrations Carbon Dioxide Vibrations

FT-IR

Retardation – difference in path length of two beams

Interferograms

Infrared Sources Glowbar Nernst glower Patented sources

Detectors DLaTGS (pyroelectric) MCT (semiconductor/quantum well) Thermodetectors ( not used for FT-IR, response time is too slow) –Thermocouple –Bolometer –Thermister

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

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.

ATR / Evanescent wave

Saturated vs. Unsaturated

Alcohols

Ketones and Aldehydes

Carboxylic Acids

Ethers

Esters

Unknowns

Raman Spectroscopy Chapters 18

Elastic scattering Photon scattered at same as incident photon Inelastic scattering Photon scattered at different as incident photon

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

Raman Selection Rule  with vibration Polarizability changes with bond length/vibration Change in bond length

Gaussian Calculations CO 2 SF 6 Chloroform

kT I mportant concept in Thermo and Stat Mech

Vibrational Selection Rules RamanInfrared

90° Scattering Instrumentation

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.

Resonance Raman

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.

FT-Raman

Fiber-Optic Raman Spectrometer BP=band pass filter BR=band rejection filter

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

Improving Raman Collection Efficiency

Crystal Hydrate Structure

Calibration - R AT - R MT

Phase Transformation upon Water Addition Raman Shift / cm-1 Int immediately 3 min 6 min 9 min 12 min 15 min 18 min

Apply Calibration to get Kinetic Transformation Profile