Boltzmann Distribution

Transcription

1 Boltzmann Distribution 0,4 N 0,3 0,2 T1 T2 T3 Τ 1 >Τ 2 >Τ 3 0,1 0, Energy

2 Electronic transitions hν hν E 2 E 1 induced Absorption spontaneous Emission induced Emission Β 12 Α 21 Β 21 Einstein coefficients

3 Black-Body Radiation A blackbody is a hypothetical object that absorbs all incident electromagnetic radiation while maintaining thermal equilibrium. The Quantum of Energy The Planck Distribution Law ρ ν ) 8 π h = c ν ( 3 h ν / kt e 3-1

4 Atomic Spectroscopy Hydrogen Helium Oxygen Xenon

5

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7 Selection Rules Δ n: without exceptions Δ l = ± 1 Δ m = 0, ± 1 Δ s: without exceptions

8 L ight A mplification by S timulated E mission of R adiation

9 Laserresonator

10 Population inversion hν b a

11 3 - levels 4 - levels E 3 E 2 pumping E 1 τ 3 fast τ 2 induced Emission (lasing) E 4 E 3 pumping E 2 E 1 fast τ 4 fast induced τ 2 Emission (lasing) τ 3 τ 2 >> τ s >> 10-8 s τ 3>> τ s >> 10-8 s

12 Different Lasers Laser Wavelength Power/Pulse Characteristics Applications Rubin Al 2 O 3 /Cr nm CW: 5W Puls:10 6, 10 6 W (1-3 ms) Puls:10 9 W(10ns) Pump: Photons 3-levels Dermathology: YAG Y 3 Al 2 O 15 /Nd nm CW: 10 3 W Puls:10 8 W (10 ns) Pumpe: Fotonen 4-levels Medicals, Research He-Ne 632.8nm W complicated. Laserprinter, Barcodescanners CO nm 9600nm CW: W Puls:10 2, 10 3 ns 10 5 W Vibration levels Industry dyelaser nm CW: 10-1 W Puls:10 5 W (6 ns) Vibration Sub-levels Spectroscopy Others: Titanium-Saphir-laser, Diodelaser, Excimerlaser

13 He Ne Laser nm Spectrum of a helium neon laser Spectrum of a helium neon laser

14 Rubinlaser (Al 2 O 3 -Wirtskristall (Saphir/Korund), dotiert mit Chromionen)

15 Carbondioxide laser

16 hν hν hν e - Valence Energy: hc/λ: 4eV 1.8eV 1eV Core UPS XPS AES Photoelectron Spectroscopy

17 Molecular Spectroscopy

18 rotating polar 2-atoms Molecule x - µ does not change. µ it changes!!!. vibrating polar 2-atoms Molecule + - µ it also changes.

19 Terms-schema and Spectrum of rotations transitions

20 Vibrations transitions between Two electronic states by a biatomic Molecule. Energy Excited electronic states Intensity distribution of vibrations transitions according to the Franck- Condon-Principle Ground electronic state Intensity Nuclear coordinates Vibrational states Energy

21 Infrared Spectroscopy ΔJ=-1 ΔJ=+1 ΔJ=0 (not allowed)

22 Raman-Effect Elastic collision of Photons Stokes-Ramandispersion Rayleighdispersion Anti-Stokes- Raman-dispersion

23 Molecules having Symmetry centers:! Vibration transitions symmetric to the symmetry center not allowed at IR spectra.! Vibration transitions antisymmetric to the symmetry center not allowed at Raman spectra.

24 Spectroscopies according to the wavelength EM-beam Wavelength Frequency range Wave number in cm 1 Energy range in kj/mol Radio Waves 100 m 1 m 3 MHz 300 MHz , Microwaves 1 m 1 cm 300 MHz 30 GHz 0, ,01 Microwaves 1 cm 100 µm 30 GHz ,01 1 Infrared 100 µm 1 µm Hz Hz Visible, UV 1 µm 10 nm Hz Hz X-Rays 10 nm 100 pm Hz Hz Gamma Rays 100 pm 1 pm Hz Hz

25 EM-beam Properties analysed Spectroscopic Method Radio Waves Microwaves Changes on the nuclear spin Changes on the electron spin Nuclear Magnetic resonance spectroscopy (NMR) Electronspin resonance spectroscopy (ESR/EPR), Ramsey-Spectroscopy (Atoms clocks) Microwaves Changes on the rotation states Microwave spectroscopy Infrared Visible, UV X-Rays Changes on the vibration states Changes on the electronic states (Outer electrons) Changes on the electronic states (inner electrons) VIbrationalspectroscopiy; (Infraredspectroscopy (IR) and Ramanspectroscopy, UV/VIS-Spectroscopy (UV/Vis), Fluorescence spectroscopy; Ultrashorttime-Spectroscopiy; Atomspectroscopy X-Ray spectroscopy (XRS); Electron spectroscopy; Auger-Electron-Spectroscopc (AES); Mößbauer-Spectroscopy Gamma Rays Changes on the nuclear states) Gammaspectroscopy