1. Near Infrared (NIR) Spectroscopy Instrumentation Paul 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

4. Content Spectroscopy? Instrumentation Modes of measurement

5. Content Spectroscopy? Instrumentation Modes of measurement

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

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

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

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

10. 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

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

12. Some useful constants q e = 1.602176462*10 -19 As m e = 9.10938188*10 -31 Kg c = 2.99792458*10 8 m/s h = 6.62606876*10 -34 Js 1 Joule to Electronvolt 6.241506363094028*10 18

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

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

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

16. 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

17. E h Ground level First excited level Quantized energy levels

18. What can be measured? Emission Absorption Fluorescence

19. E h   Ground level First excited level Emission Thermal

20. E h   Ground level First excited level Absorption Thermal

21. E hh Ground level First excited level Fluorescence h out

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

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

24. Special topics Polarization Time resolved spectroscopy

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

26. Vibrational spectroscopy

27. 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

28. De = 5 b = 0.5

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

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

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

32. This was diatomic molecules Polyatomic molecules: M=3N-6 quantized vibration modes M=3N-5 linear molecules (N=1) N=3, M=3 H 2 O, H 2 S, SO 2 N=4, M=6 etc

33. Triatomic molecules G(a,b,c)=v 1 (a+1/2) + v 2 (b+1/2) + v 3 (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)

34. ac b Combination band Overtone Ground level Hot band Fundamental (0,0,0) (1,0,0) (2,0,0) (0,1,0) (0,2,0) (0,0,1) (0,0,2)

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

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

37. Why cm -1 ? Additive

38. S0 2 wavenumberband 519v2 606v1-v2 1151v1 1361v3 1871v2+v3 22962v1 2499v1+v3

39. Thermal radiation Planck’s law W( ) = c 1 -5 [exp(c 2 -1 T -1 )-1] T °K c1 = 1.91*10 -12 c2 = 1.438*10 4   m

40. mm Radiance 4000 K (Tungsten melts) 3500 K 3000 K 2500 K 2000 K

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

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

43. Energy supply Photon Thermal Electron - Proton + Ion + -

44. Optics Electron optics Ion optics

45. Techniques Electron microscopy Electron spectroscopy Mass spectrometry Ion microscopy

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

47. Transmission Readout electronics Detector Sample cell Mono- chromator Radiation source I0I0 ItIt

48. Lambert-Beer-Bouguer law Transmission Absorbance T = I t / I 0 A = log 10 ( I 0 / I t ) = -log 10 (I t / I 0 )

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

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

51. Reflection Readout electronics Detector(s) Sample cell Mono- chromator Radiation source I0I0 IrIr

52. Lambert-Beer-Bouguer law Reflection Pseudoabsorbance R = I r / I 0 A* = -log 10 (I r / I 0 )

53. Content Spectroscopy? Instrumentation Modes of measurement

54. What can be changed? Radiation source Monochromator Sample cell Detector

55. Radiation source Tungsten-halogen lamp (Car type) Coated tungsten SiC Laser(s) LEDs LED arrays

56. ln(Wavelength),  m ln(Energy flux) 3000K 1000K 0.21

57. Wavelength, m Energy flux 1000 1150 1300 1520 LEDs

58. What can be changed? Radiation source Monochromator Sample cell Detector

59. Monochromator ”Glass filter” Interference filters Prism Grating Interferometer Electrooptical

60. Monochromator ”Glass filter” not selective Interference filters Prism too primitive, never used Grating Interferometer Electrooptical

61. Interference filter Glass High RI coating Low RI coating Multiple reflections

62. Tilting interference filter Glass High RI coating Low RI coating Different pathlengths

63. There are also gradual interference filters Disk with increasing thickness Rotate for new wavelength bands

64. Filter wheel Readout electronics Detector(s) Sample cell Radiation source Filter wheel

65. Grating Mirror staircase Pathlength difference

66. Grating Polychromatic Monochromatic Rotate Entrance slit Exit slit

67. Interferometer Fixed mirror Moving mirror Semitransparant mirror (50%) Detector Sample

68. Interferometer Fixed mirror Moving mirror Semitransparant mirror (50%) Detector (interferogram) a b Wavelengths for which b-a = whole cycle reach detector

69. Interferometer Interferogram Fourier transform Spectrum

70. What can be changed? Radiation source Monochromator Sample cell Detector

72. Content Spectroscopy? Instrumentation Modes of measurement

73. This is a real strong point of NIR spectroscopy. There are many modes of measurement: Transmission Diffuse reflection Fiber optic based -Transflection -Interaction

74. Det Integrating sphere Det Fiberoptic Mirror

75. Transflectance probe Fiber bundleSapphire mirror

76. Mixed solutions Use tunable laser instead of monochromator (more lasers?) Use LED’s in different wavelengths instead of monochromator Use array of detectors instead of scanning monochromator DIODE ARRAY

77. Grating Polychromatic Entrance slit Diode array

78. Filter wheel instrument with interference filters

79. Interferometric instrument

81. Process NIR spectrometer based on moving grating

82. Transmision instrument

83. Sample changer for seeds (transmission)

84. Diffuse reflectance instrument (rotating cup)