Gang Wang Instrumental_Week2_CH6-2010

Gang Wang Instrumental_Week2_CH6-2010 - Skoog Chapter 6...

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Skoog–Chapter 6 Introduction to Spectrometric Methods y General Properties of Electromagnetic Radiation (EM) y Wave Properties of EM y Quantum Mechanical Properties of EM y Quantitative Aspects of Spectrochemical Measurements y Spectrometric method atomic y molecular spectroscopy y Interaction of electromagnetic radiation and matter y Interaction between matter and other forms of energy y Measurement of intensity of radiation by photoelectronic transducer or other electronic device Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what we call the visible spectrum, or light.
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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 Sinusoidal wave model: wavelength, frequency, velocity and amplitude Particle model: frequency of the wave is proportional to the particle's energy
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Relationship between various wave properties C ν λ i = ‐‐‐‐‐ η i Where ν = frequency in cycles/s or Hz Determined by source and remain invariant λ i = wavelength in medium i η i = refractive index of medium i C = speed of light in vacuum (2.99 x 10 10 cm/s) Depends upon composition medium EM slows down in media other than vacuum because electric vector interacts with electric fields in the medium (matter) Æ liquids, in gases (air) velocity similar to vacuum Wave Equation y = A sin ( ω t + φ ) Where y = magnitude of wavelength at time t A = amplitude of maximum value for y ω = angular frequency = 2 πυ φ = 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 + φ 1 ) + A 2 sin ( ω 2 t + φ 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 180 o 360 o 540 o 720 o 900 o Wave 1 Wave 2 Resultant wave Phase angle difference between is zero α 1 - α 2 = 0 o Amplitude
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When α 1 α 2 = 180 o or 540 o adding of waves gives Maximum Destructive Interference
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Gang Wang Instrumental_Week2_CH6-2010 - Skoog Chapter 6...

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