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INTRO TO SPECTROSCOPIC METHODS (Chapter 6) NATURE OF LIGHT AND INTERACTION WITH MATTER Electromagnetic Radiation (i.e., “light”) –Wave-particle duality Particle properties (photons or quanta) Wave properties (sinusoidal waves)
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Plane-polarized em radiation of wavelength λ SHC, 6e, Fig. 6-1 A (in watts) Frequency ( ν ) in Hz or s -1 ν = c/λ where c = 3.00 x 10 8 m/s
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Electromagnetic spectrum showing representative molecular processes Analogous to SHC, 6e, Fig. 6-3 and Table 6-1
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MATH DESCRIPTION OF A WAVE Equation of a sine wave: Where the angular velocity: By substitution: 1) SUPERPOSITION OF WAVES Two or more waves interact either through: Constructive interference or Constructive interference or Destructive Interference Destructive Interference
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SHC, 6e, Fig. 6-4: Constructive and destructive interference. 0°0°90°180°
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Fourier Transform (FT): a math operation that reduces a complex wave to the sum of simple sine and cosine terms. Fourier Transform (FT): a math operation that reduces a complex wave to the sum of simple sine and cosine terms. Used in signal analysis (e.g., FT-IR, FT-NMR, etc) Used in signal analysis (e.g., FT-IR, FT-NMR, etc) 2) DIFFRACTION Consequence of interference (SHC, 6e, Fig. 6-8) Consequence of interference (SHC, 6e, Fig. 6-8) 3) COHERENCE Source output has the same ν ’s and λ ’s Source output has the same ν ’s and λ ’s Phase relationships remain constant in time Phase relationships remain constant in time
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4) TRANSMISSION OF RADIATION c = 3.00 x 10 8 m/s in a vacuum c = 3.00 x 10 8 m/s in a vacuum Light slows in other media Light slows in other media Index of refraction: Index of refraction: for liquids = 1.3 – 1.8; for solids = 1.3 – 2.5 or higher for liquids = 1.3 – 1.8; for solids = 1.3 – 2.5 or higher 5) REFRACTION OF RADIATION The bending of light as it passes from one medium to another The bending of light as it passes from one medium to another
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SHC, 6e, Fig. 6-10 Refraction of Light M1M1 M2M2 Snell’s Law:
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less dense more dense medium bent towards normal to interface more dense less dense medium bent away from normal to interface 6) REFLECTION OF RADIATION Two types: Specular (from a smooth surface) Diffuse (from a rough surface)
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Optical Fiber Construction and Principle of Operation } glass or plastic Any ray entering within the cone of acceptance will be totally internally reflected
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7) SCATTERING OF RADIATION –Rayleigh from very small particles with diameters < λ intensity ~ 1/λ 4 –Tyndall effect from colloidal sized particles can be observed with naked eye –Raman radiation undergoes frequency changes decreased frequency (Stokes) increased frequency (anti-Stokes)
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8) POLARIZATION OF RADIATION –Plane-polarized: (end-on-view) –Result: polarizer vertically polarized electric vector SHC, 6e, Fig. 6-11 & 6-12 Polarization of Light
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