lec08.intro_spectr

lec08.intro_spectr - INTRODUCTION TO SPECTROSCOPY...

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INTRODUCTION TO SPECTROSCOPY
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Spectroscopy Spectroscopy is a general term referring to the interactions of various types of electromagnetic radiation with matter. Exactly how the radiation interacts with matter is directly dependent on the energy of the radiation.
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Spectroscopy The higher energy ultraviolet and visible wavelengths affect the energy levels of the outer electrons. Radio waves are used in nuclear magnetic Resonance and affect the spin of nuclei in a magnetic field. Infrared radiation is absorbed by matter resulting in rotation and/or vibration of molecules.
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THE ELECTROMAGNETIC SPECTRUM Important: As the wavelength gets shorter, the energy of the radiation increases.
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PARTICLE NATURE OF RADIATION Electromagnetic radiation is also described as having the properties of particles. Molecules exist in a certain number of possible states corresponding to definite amounts of energy. Molecules can absorb energy and change to a higher energy level called the excited state. The amount of energy absorbed in this transition is exactly equal to the energy difference between the states.
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Energy Level Diagram for an Atom of Sodium E 0 E 1 E 2 ENERGY Ground State 590 nm 330 nm
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Energy Level Diagram for a Simple Molecule E 0 E 1 E 2 ENERGY Ground State Excitation to the next electronic energy level caused by adsorption of specific wavelengths e4 e3 e2 e1 Vibrational Energy Levels Relaxation from the E 2 energy state to E 0 may go to different vibrational energy states, emitting different wavelengths.
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UV/VIS SPECTROSCOPY Visible (380-780 nanometers) Ultraviolet (UV) (10 – 380 nanometers). How many µm is 780 nanometers? What is the corresponding wave number? Below about 200 nm, air absorbs the UV light and instruments must be operated under a vacuum
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Absorption of ultraviolet and visible light only takes place in molecules with valence electrons of low excitation energy. e
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lec08.intro_spectr - INTRODUCTION TO SPECTROSCOPY...

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