Near Infrared (NIR) Spectroscopy Instrumentation Paul Geladi

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

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 = hn • E = hc/l • Planck’s constant 6.63 10-34

12. 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

13. Units • Joule (energy) • Electron volt (KeV) • Wavelength (nm, mm, 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) = electron Xray UV,VIS H Cl NIR,IR UV,VIS Gamma ray

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 Quantized energy levels First excited level hn Ground level

18. What can be measured? Emission Absorption Fluorescence

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

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

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

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 Position Intensity, integral Width Energy

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

32. 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

33. 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)

34. 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

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(-DE/kT) • Ne number excited, No number ground • k Boltzmann constant 1.3806503*10-23 J/K • DE energy difference

37. Why cm-1? Additive

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

39. 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

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

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 Mono- chromator Detector Readout electronics Radiation source Sample cell

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

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

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

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