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= eV Z 2 /n 2

Energy Level Diagrams, Hydrogen 1 K eV eV eV L eV

Zeeman Effect = Splitting or emission lines if in B field

Molecular Orbitals New Energy –Bonding –Anti Bonding Hybridization New Shapes to Orbitals with hybridization 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/I o

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, λ o Electron from GS to Excited State Electron Cascades back to GS Light Emission –Different color, λ 1 I=Kε(λ o )I o Q (λ 1 ) Q=quantum efficiency K device constant Quenching at High C, Q 

Fluorescence I=Kε(λ o )I o Q (λ 1 ) 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