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Instrumental Lecture 3

Instrumental Lecture 3 - Skoog Chapter 6 Intro to...

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Skoog – Chapter 6 Intro to Spectrometric Methods General Properties of Electromagnetic Radiation (EM) Wave Properties of EM Quantum-Mechanical Properties of EM Quantitative Aspects of Spectrochemical Measurements

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R O Y G B V Gamma Ray Spectroscopy X-Ray Absorption, Fluorescence UV-vis Absorption, Fluorescence Infrared Absorption Spectroscopy Microwave Absorption Spectroscopy NMR EPR Nuclear Transitions Inner Shell Electrons Outer Shell Electrons Molecular Vibrations Molecular Rotations Spin States Low Energy High Energy
Spectroscopy = methods based on the interaction of electromagnetic radiation (EM) and matter Electromagnetic Radiation = form of energy with both wave and particle properties EM moves through space as a wave Most interactions of EM with matter are best understood in terms of electric vector

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Relationship between various wave properties C ν λ i = ----- η i Where ν = frequency in cycles/s or Hz λ i = wavelength in medium i η i = refractive index of medium i C = speed of light in vacuum (2.99 x 1 0 1 0 cm/s) EM slows down in media other than vacuum because electric vector interacts with electric fields in the medium (matter) this effect is greatest in solids & liquids, in gases (air) velocity similar to vacuum
Wave Equation y = A sin ( ω t + α ) Where A = amplitude ω = angular frequency α = phase angle t = time For a collection of waves the resulting position y at a given t can be calculated by y = A 1 sin ( ω 1 t + α 1 ) + A 2 sin ( ω 2 t + α 2 ) + …

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Interference - amplitude of the resulting wave depends on phase difference α 1 - α 2 Constructive Interference waves add Destructive Interference waves cancel
At α 1 - α 2 = 0 o adding of waves gives Maximum Constructive Interference 0 o 1 80 o 360 o 540 o 720 o 900 o Wave 1 Wave 2 Resultant wave Phase angle difference between Wave 1 & Wave 2 is zero α 1 - α 2 = 0 o Amplitude

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When α 1 - α 2 = 1 80 o or 540 o adding of waves gives Maximum Destructive Interference 0 o 1 80 o 360 o 540 o 720 o 900 o Wave 1 Wave 2 Resultant wave Phase angle difference between Wave 1 & Wave 2 is 1 80 o ( α 1 - α 2 = 1 80 o ) Amplitude
Diffraction = EM going past an edge or through a slit (2 edges) tends to spread The combination of diffraction effects & interference effects are important in spectroscopy for 1 )diffraction gratings 2) slit width considerations

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Refraction = change in velocity of EM as it goes from one medium to another Normal to surface Medium 1 (air) Velocity larger η = 1 .00 Medium 2 (glass) Velocity smaller η = 1 .50 Incident ray Ф 1 Ф 2 Refracted ray Original direction Ray bent toward normal
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Instrumental Lecture 3 - Skoog Chapter 6 Intro to...

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