Coursehero >> Illinois >> Ill. Chicago >> CHEM 52409

Course Hero has millions of student submitted documents similar to the one below including study guides, homework solutions, papers, exam answer keys and textbook solutions.

524 Chem Lecture Notes (Section 17)--2009 For pdf of these notes, click here For HTML of 2005 notes, click here XIII. Molecular Light Scattering and Raman Spectroscopy (Read Ch. 16) A. Elastic Scattering o = s 1) Raleigh Scattering scatters are small compared to s - same frequency, Intensity ~ -4, ~ 2 (polarizability) 2) Debye/Mie more anisotropic spatial variation indicates size and shape B. Inelastic - o s 1) Brillouin scatter from phonons (thermal density fluctuation) 2) Raman scatter from molecular excited states vibrations most often (also rotations, low lying electronic states) C. Raman s = o vib(rot) (+) = anti stokes (-) = stokes (energy into molecule) -- qualitative big use (like IR) identify/characterize -- qualitative particularly difficult standards 80 IR 60 Arbitrary Y 40 20 Raman 3000 2500 2000 Raman Shift (cm-1) 1500 1000 0 File # 2 : SILICONE - capable of small volumes/but require relatively high concentration --Complementary to IR, tend to opposite selection rules, different intensities ~[ / Q]2 1. Instruments many used to be homemade, construct from components Commercial components a. Rebuilt emission higher res needed/very high sensitive? -- Ar laser typical excite visible, 488 or 514 nm /now YAG (doubled at 532) or diodes various places, and special FRED lasers, double to UV -- PMT and photon count typical /now CCD universal with spectrograph simultaneous detection spectrum -- 90 Scatter typical (include back reflection), 180 sometimes more efficient, better for imaging or microscopy -- monochromator double (even triple) 1/2 > 1m typical (scatter light) /now single spectrograph + CCD + holographic filter for laser -- microscope (180 ) possible, fine focus possible due to shorter wavelength, 0 -- polarization important (polarized, ||, and depolarized transitions, Raman ) is 2-photon, so relative polarization of ex and s beams important Polarization ratio: = I /I|| -- < 7/8 (or < for different excitation geometry) means mode is polarized, can tell symmetry of transition b. Multichannel systems fixed resolution -- go for speed/ S/N by averaging -- diode array works/CCD can be better, bigger slit image -- can do time dependence with gate < s c. FT Raman near IR laser (700 nm > 1 ) -- lose as 4 -- gain from multiplex Link to write-up on methods, Henry Bujis -- big advantage eliminate. fluorescence -- big application materials/bio/complex sample -- YAG: need InGaAs (~1.8 ) on Ge (~1.6 ) detector limit -- Ti: Sapphire GaAs PMT works -- back scatter aid illuminate round pattern -- filter Rayleigh is vital importance 2. Sampling, multiple styles a) 90 capillary or tube is fine/optical quality b) 180 cuvette, polish bottom c) flow narrow device/jet d) cool stir/spin/blow cold N2 -- crystal mount in dewar, on a cold finger (platform) 3. Resonance Raman less analytically important a) excite a real absorption state b) seek info about vibrations and excited state c) enhance intensity more dilute samples 4. SERS surface enhancement by analyte on metal (Au typ) surface rougher 5. CARS, etc many non-linear possibilities utilize multiple photon excitations 6. Time dependent if signal enhanced can excite w/ps or ns laser and see time dependent processes 7. Raman optical activity differential scatter of left and right circular polarized light (only for molecules that are chiral) -- instrument figures, 180o back scatter, transmission spectrograph, very good conventional design: L.D. Barron (note: W.Hug developed a more complex design, currently marketed by BioTools that has improvements) Data: helicene (W. Hug below) Lysozyme in water (BioTools)

Find millions of documents here - Study Guides, Homework Solutions, Papers, Exam Answer Keys and more. Course Hero has millions of course related materials that will enable you to learn better, faster and get an A in all your courses.
Below is a small sample set of documents: