Molecular Spectra

Terry A. Ring

Chemical Engineering

University of Utah

EM Spectrum

• 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

hc

n

Z

n

ZeVE

ab

2

2

2

2

6.13

Energy Level Diagrams, Hydrogen

1 K

2

34

-13.6 eV

-3.40 eV

-1.51 eV

L

-0.85 eV

hc

n

Z

n

ZeVE

ab

2

2

2

2

6.13

Zeeman Effect = Splitting or emission lines if in B field

H field

Bm

emE

el 2

Molecular Orbitals

• New Energy– Bonding

– Anti Bonding

• Hybridization• New Shapes to

Orbitals with hybridization

•• •

•1s 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

• 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 π-electron 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 (x-ray)

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

• Wavelength-dispersive XRF

XRF Detectors

• Energy-dispersive XRF– Semiconductor

• Wavelength dispersive XRF– Scintilation Counter

XRF Analysis

• Samples can be in any form– Solid– Powder– Liquid