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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.

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Presentation on theme: "INTRO TO SPECTROSCOPIC METHODS (Chapter 6) NATURE OF LIGHT AND INTERACTION WITH MATTER Electromagnetic Radiation (i.e., “light”) –Wave-particle duality."— Presentation transcript:

1 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)

2 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

3 Electromagnetic spectrum showing representative molecular processes Analogous to SHC, 6e, Fig. 6-3 and Table 6-1

4 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

5 SHC, 6e, Fig. 6-4: Constructive and destructive interference. 0°0°90°180°

6 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

7 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

8 SHC, 6e, Fig. 6-10 Refraction of Light M1M1 M2M2 Snell’s Law:

9 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)

10 Optical Fiber Construction and Principle of Operation } glass or plastic Any ray entering within the cone of acceptance will be totally internally reflected

11 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)

12 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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