Near Infrared (NIR) Spectroscopy Instrumentation Paul Geladi - PowerPoint PPT Presentation

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Near Infrared (NIR) Spectroscopy Instrumentation Paul Geladi

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  1. Near Infrared (NIR) Spectroscopy InstrumentationPaul Geladi

  2. Paul Geladi Head of Research NIRCE Chairperson NIR Nord Unit of Biomass Technology and Chemistry Swedish University of Agricultural Sciences Umeå Technobothnia Vasa paul.geladi @ btk.slu.se paul.geladi @ uwasa.fi

  3. Content • Spectroscopy? • Instrumentation • Modes of measurement

  4. Content • Spectroscopy? • Instrumentation • Modes of measurement

  5. Content • Spectroscopy? • Energy levels in atoms, molecules, crystals • Example IR-NIR calculations • Related techniques

  6. Content • Spectroscopy? • Energy levels in atoms,molecules, crystals • Example IR-NIR calculations • Related techniques

  7. Spectroscopy • Interaction of radiation and matter • Electromagnetic radiation • Gases, liquids, solids, mixtures • Heterogeneous materials

  8. Electromagnetic radiation Cosmic Gamma Xray UV VIS NIR IR Micro Radio

  9. Electromagnetic radiation • Cosmic > 2500 KeV • Gamma 10-2500 KeV • Xray 0.1-100 KeV • Ultraviolet 10-400 nm • Visible 400-780 nm • Near Infrared 780-2500 nm • Infrared 2500-15000 nm • Microwave GHz • Radio MHz-KHz

  10. Why interaction? • Photon energy matches some energy level • E = hn • E = hc/l • Planck’s constant 6.63 10-34

  11. Some useful constants • qe= 1.602176462*10-19 As • me = 9.10938188*10-31 Kg • c = 2.99792458*108 m/s • h = 6.62606876*10-34 Js • 1 Joule to Electronvolt 6.241506363094028*1018

  12. Units • Joule (energy) • Electron volt (KeV) • Wavelength (nm, mm, mm) • Inverse cm (cm-1) • Frequency (GHz,MHz,KHz)

  13. Content • Spectroscopy? • Energy levels in atoms,molecules, crystals • Example IR-NIR calculations • Related techniques

  14. HCl molecule (no true sizes) = electron Xray UV,VIS H Cl NIR,IR UV,VIS Gamma ray

  15. Photon-matter interaction • Atomic nucleus = gamma ray • Inner electron = Xray • Outer electron, chemical single bond = UV • Chemical double, triple bond = UV,VIS • Molecular vibration overtone = NIR • Molecular vibration = IR • Molecular rotation = Micro

  16. E Quantized energy levels First excited level hn Ground level

  17. What can be measured? Emission Absorption Fluorescence

  18. E Emission First excited level Thermal hn Ground level

  19. E Absorption First excited level Thermal hn Ground level

  20. E Fluorescence First excited level hn hn out Ground level

  21. Techniques? • Gamma spectrometry • Instrumental neutron activation analysis • Xray spectrometry • UV-VIS spectrometry (AES,AAS,ICP...) • NIR spectrometry • IR spectrometry • Raman spectrometry • Microwave spectrometry

  22. What can be used? Intensity Position Intensity, integral Width Energy

  23. Special topics • Polarization • Time resolved spectroscopy

  24. Content • Spectroscopy? • Energy levels in atoms,molecules, crystals • Example IR-NIR calculations • Related techniques

  25. Vibrational spectroscopy

  26. Morse curves The Morse curve describes the potential energy V of a diatomic molecule as a function of interatomic distance x. V = De [1-exp(-bx)]2

  27. De = 5 b = 0.5

  28. If the atoms go far apart the bond breaks. It is impossible to press the atoms close together. Enormous amounts of energy are needed.

  29. De = 10 b = 0.4 Zero = equilibrium distance

  30. F Fundamental O1 First overtone O2 Second overtone Quantum levels = discrete O2 O1 F

  31. This was diatomic molecules Polyatomic molecules: M=3N-6 quantized vibration modes M=3N-5 linear molecules (N=1) N=3 , M=3 H2O, H2S, SO2 N=4 , M=6 etc

  32. Triatomic molecules • G(a,b,c)=v1(a+1/2) + v2(b+1/2) + v3(c+1/2) • Energy levels • a=b=c=0 (0,0,0) • a=1 b=c=0 (1,0,0) • a=2 b=c=0 (2,0,0) • a=0 b=1 c=0 etc (0,1,0)

  33. Hot band Overtone Combination band (0,0,2) Fundamental (0,2,0) (0,0,1) (2,0,0) (0,1,0) (1,0,0) (0,0,0) Ground level a c b

  34. Intensity • Some transitions are more probable • Gives more intense bands • Fundamentals in Gas phase • Overtones in liquid,solid • Combination bands in liquid, solid

  35. Hot bands • Only exist because of thermal excitation • Boltzmann • Ne = No exp(-DE/kT) • Ne number excited, No number ground • k Boltzmann constant 1.3806503*10-23 J/K • DE energy difference

  36. Why cm-1? Additive

  37. S02 wavenumber band 519 v2 606 v1-v2 1151 v1 1361 v3 1871 v2+v3 2296 2v1 2499 v1+v3

  38. Thermal radiation • Planck’s law • W(l) = c1l-5[exp(c2l-1 T-1)-1] • T °K • c1 = 1.91*10-12 • c2 = 1.438*104 • lmm

  39. Radiance 4000 K (Tungsten melts) 3500 K 3000 K 2500 K 2000 K mm

  40. Planck curves More total energy for high temperature More UV for high temperature More flat curve for low temperature

  41. Content • Spectroscopy? • Energy levels in atoms,molecules, crystals • Example IR-NIR calculations • Related techniques

  42. Energy supply • Photon • Thermal • Electron - • Proton + • Ion + -

  43. Optics • Electron optics • Ion optics

  44. Techniques • Electron microscopy • Electron spectroscopy • Mass spectrometry • Ion microscopy

  45. Transmission Mono- chromator Detector Readout electronics Radiation source Sample cell

  46. Transmission Mono- chromator I0 It Detector Readout electronics Radiation source Sample cell

  47. Lambert-Beer-Bouguer lawTransmissionAbsorbance T = It / I0 A = log10 ( I0 / It) = -log10 (It / I0)

  48. Lambert-Beer-Bouguer law A = klC l = path length k = constant C = concentration

  49. Reflection Mono- chromator Detector(s) Readout electronics Radiation source Sample cell