Boltzmann Distribution 0,4 N 0,3 0,2 T1 T2 T3 Τ 1 >Τ 2 >Τ 3 0,1 0,0 0 1 2 3 4 5 6 7 8 9 10 Energy
Electronic transitions hν hν E 2 E 1 induced Absorption spontaneous Emission induced Emission Β 12 Α 21 Β 21 Einstein coefficients
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
Atomic Spectroscopy Hydrogen Helium Oxygen Xenon
Selection Rules Δ n: without exceptions Δ l = ± 1 Δ m = 0, ± 1 Δ s: without exceptions
L ight A mplification by S timulated E mission of R adiation
Laserresonator
Population inversion hν b a
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 3 10-3 s >> 10-8 s τ 3>> τ 2 10-3 s >> 10-8 s
Different Lasers Laser Wavelength Power/Pulse Characteristics Applications Rubin Al 2 O 3 /Cr +3 694.3 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 +3 1064 nm CW: 10 3 W Puls:10 8 W (10 ns) Pumpe: Fotonen 4-levels Medicals, Research He-Ne 632.8nm 10-3 - 10-2 W complicated. Laserprinter, Barcodescanners CO 2 10600nm 9600nm CW: 10 10 4 W Puls:10 2, 10 3 ns 10 5 W Vibration levels Industry dyelaser 650-1000nm CW: 10-1 W Puls:10 5 W (6 ns) Vibration Sub-levels Spectroscopy Others: Titanium-Saphir-laser, Diodelaser, Excimerlaser
He Ne Laser 632.8 nm Spectrum of a helium neon laser Spectrum of a helium neon laser
Rubinlaser (Al 2 O 3 -Wirtskristall (Saphir/Korund), dotiert mit Chromionen)
Carbondioxide laser
hν hν hν e - Valence Energy: hc/λ: 4eV 1.8eV 1eV Core UPS XPS AES Photoelectron Spectroscopy
Molecular Spectroscopy
rotating polar 2-atoms Molecule + - + x - µ does not change. µ it changes!!!. vibrating polar 2-atoms Molecule + - µ it also changes.
Terms-schema and Spectrum of rotations transitions
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
Infrared Spectroscopy ΔJ=-1 ΔJ=+1 ΔJ=0 (not allowed)
Raman-Effect Elastic collision of Photons Stokes-Ramandispersion Rayleighdispersion Anti-Stokes- Raman-dispersion
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.
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 10 4 0,01 10 6 10 4 Microwaves 1 m 1 cm 300 MHz 30 GHz 0,01 1 10 4 0,01 Microwaves 1 cm 100 µm 30 GHz 3 10 12 1 100 0,01 1 Infrared 100 µm 1 µm 3 10 12 Hz 3 10 14 Hz 100 10 4 1 100 Visible, UV 1 µm 10 nm 3 10 14 Hz 3 10 16 Hz 10 4 10 6 100 10 4 X-Rays 10 nm 100 pm 3 10 16 Hz 3 10 18 Hz 10 6 10 8 10 4 10 6 Gamma Rays 100 pm 1 pm 3 10 18 Hz 3 10 20 Hz 10 8 10 10 10 6 10 8
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