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)

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

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

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

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

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

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

SHC, 6e, Fig Refraction of Light M1M1 M2M2 Snell’s Law:

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)

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

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)

8) POLARIZATION OF RADIATION –Plane-polarized: (end-on-view) –Result: polarizer vertically polarized electric vector SHC, 6e, Fig & 6-12 Polarization of Light