Transcript Molecular Spectroscopy.ppt

Molecular Spectra
Terry A. Ring
Chemical Engineering
University of Utah
EM Spectrum
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X-rays
UV
Visible
IR
Microwave
Radio
waves
What is EM radiation?
Various Spectra
• UV-Vis - Excitation of π-electrons or n-electrons
• IR-Bond Vibration - Electronic Cloud Oscillation
• Fluorescence – Light Absorption moves electron from GS
to ES then light emission (different wavelength)
E= -13.6 eV Z2/n2
 Z 2 Z 2  hc
E  13.6eV  2  2  
 nb na  
Energy Level Diagrams,
Hydrogen
-0.85 eV
-1.51 eV
4
3
2
L
-3.40 eV
 Z 2 Z 2  hc
E  13.6eV  2  2  
 nb na  
1
K
-13.6 eV
Zeeman Effect = Splitting or
emission lines if in B field
e
E  ml
B
2me
H field
Molecular Orbitals
• New Energy
– Bonding
– Anti Bonding
• Hybridization
• New Shapes to
Orbitals with
hybridization
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1s
Spectrometers
• Absorption
• Emission - Absorption moves electron from GS to ES then
emission
Color Analysis
• Color Comparison
UV-Visible Spectrometer
• Absorption Spectrometer
– Direct or comparative
Accuracy of Spectrometer
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Spectral Resolution
(Bandwidth)
Δλ= s dλ/ds
Slit width = s
Precision of
prism/grating, dλ/ds
Benzene
Analysis
• UV of Benzene
Derivative
• Beer Lambert Law
• A=-log(T)= () c l
• T=I/Io
Metal Complexation
• Metal with πelectron Complex in
water solution
• Colored Solution
– Different color than
organic alone
Reagent Excess/Metal Excess
• Two Component
Analysis
• Principle
Component
Analysis
• (More than two)
Fluorescence
• Light Absorbed, λo
• Electron from GS to
Excited State
• Electron Cascades
back to GS
• Light Emission
– Different color, λ1
• I=Kε(λo)IoQ (λ1)
• Q=quantum efficiency
• K device constant
• Quenching at High C, Q
Fluorescence
• I=Kε(λo)IoQ (λ1)
• Q=quantum efficiency
• K device constant
• Quenching at High C,
– Q
– self absorption
• Fluorophore
– Chelating agents for metals
X-ray Fluorescence
• Two Steps
– Absorption of X-ray
• Elimination of
electron for k or L
shell
– Collapse of L or M
shell electron to fill
hole
• Light emission (xray)
XRF Model, K & K
Potential X-ray
Emissions
• From K shell hole
– K, K, K,
– Zeeman Effect - 1, 2, 3
• From L shell hole
– L, L, L,
Note Nomenclature Error
Generation of X-rays
• High Voltage
Electrons
• Electron Scattering
• Electron Absorption
– X-ray photo
ionization
XRF
• Energy-dispersive
XRF
• Wavelengthdispersive XRF
XRF Detectors
• Energy-dispersive
XRF
– Semiconductor
• Wavelength
dispersive XRF
– Scintilation Counter
XRF Analysis
• Samples can be in
any form
– Solid
– Powder
– Liquid