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Molecular Spectra

Molecular Spectra. Terry A. Ring Chemical Engineering University of Utah. EM Spectrum. X-rays UV Visible IR Microwave Radio waves. What is EM radiation?. Various Spectra. UV-Vis - Excitation of π-electrons or n-electrons IR-Bond Vibration - Electronic Cloud Oscillation

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Molecular Spectra

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  1. Molecular Spectra Terry A. Ring Chemical Engineering University of Utah

  2. EM Spectrum • X-rays • UV • Visible • IR • Microwave • Radio waves What is EM radiation?

  3. Various Spectra • UV-Vis - Excitation of π-electrons or n-electrons • IR-Bond Vibration - Electronic Cloud Oscillation • Fluorescence – Light Absorption moves electron from GS to ES then light emission (different wavelength)

  4. E= -13.6 eV Z2/n2

  5. Energy Level Diagrams, Hydrogen -0.85 eV 4 -1.51 eV 3 L -3.40 eV 2 K -13.6 eV 1

  6. Zeeman Effect = Splitting or emission lines if in B field

  7. Molecular Orbitals • • 1s • New Energy • Bonding • Anti Bonding • Hybridization • New Shapes to Orbitals with hybridization 1s • •

  8. Spectrometers • Absorption • Emission - Absorption moves electron from GS to ES then emission

  9. Color Analysis • Color Comparison

  10. UV-Visible Spectrometer • Absorption Spectrometer • Direct or comparative

  11. Accuracy of Spectrometer • Spectral Resolution • (Bandwidth) • Δλ= s dλ/ds • Slit width = s • Precision of prism/grating, dλ/ds Benzene

  12. Analysis • UV of Benzene Derivative • Beer Lambert Law • A=-log(T)= () c l • T=I/Io

  13. Metal Complexation • Metal with π-electron Complex in water solution • Colored Solution • Different color than organic alone

  14. Reagent Excess/Metal Excess • Two Component Analysis • Principle Component Analysis • (More than two)

  15. Fluorescence • Light Absorbed, λo • Electron from GS to Excited State • Electron Cascades back to GS • Light Emission • Different color, λ1 • I=Kε(λo)IoQ (λ1) • Q=quantum efficiency • K device constant • Quenching at High C, Q

  16. Fluorescence • I=Kε(λo)IoQ (λ1) • Q=quantum efficiency • K device constant • Quenching at High C, • Q • self absorption • Fluorophore • Chelating agents for metals

  17. X-ray Fluorescence • Two Steps • Absorption of X-ray • Elimination of electron for k or L shell • Collapse of L or M shell electron to fill hole • Light emission (x-ray)

  18. XRF Model, K & K

  19. Potential X-ray Emissions • From K shell hole • K, K, K, • Zeeman Effect - 1, 2, 3 • From L shell hole • L, L, L, Note Nomenclature Error

  20. Generation of X-rays • High Voltage Electrons • Electron Scattering • Electron Absorption • X-ray photo ionization

  21. XRF • Energy-dispersive XRF • Wavelength-dispersive XRF

  22. XRF Detectors • Energy-dispersive XRF • Semiconductor • Wavelength dispersive XRF • Scintilation Counter

  23. XRF Analysis • Samples can be in any form • Solid • Powder • Liquid

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